Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session KP1: Poster SessionPoster
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Room: Exhibit Hall B |
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KP1.00001: Numerical Study of Laminar Flow over Acoustic Cavities Matthew Owen, Gary Cheng Fluid flow over an open cavity often emits acoustic waves with certain natural frequencies dependent on the geometry of the cavity and the properties and flow conditions of the fluid. Numerical studies of this kind, Computational Aeroacoustics (CAA), pose a grave challenge to the accuracy and efficiency of numerical methods. This project examines the Space-Time Conservation Element Solution Element (CESE) method developed by Dr. S.C. Chang at NASA GRC and compares numerical results of two-dimensional flow to previous experimental data found in literature. The conclusion the project reached is that the test data agrees well with one of the modes of the predicted frequencies, and that further testing is needed to be able to match experimental results. [Preview Abstract] |
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KP1.00002: Implementation of CPFD to Control Active and Passive Airfoil Propulsion Jay Young, Daniel Asselin, Charles Williamson The fluid dynamics of biologically-inspired flapping propulsion provides a fertile testing ground for the field of unsteady aerodynamics, serving as important groundwork for the design and development of fast, mobile underwater vehicles and flapping-wing micro air vehicles (MAVs). There has been a recent surge of interest in these technologies as they provide low cost, compact, and maneuverable means for terrain mapping, search and rescue operations, and reconnaissance. Propulsion by unsteady motions has been fundamentally modeled with an airfoil that heaves and pitches, and previous work has been done to show that actively controlling these motions can generate high thrust and efficiency (Read, Hover {\&} Triantafyllou 2003). In this study, we examine the performance of an airfoil with an actuated heave motion coupled with a passively controlled pitch motion created by simulating the presence of a torsional spring using our cyber-physical fluid dynamics (CPFD) approach (Mackowski {\&} Williamson 2011, 2015, 2016). By using passively controlled pitch, we have effectively eliminated an actuator, decreasing cost and mass, an important step for developing efficient vehicles. In many cases, we have achieved comparable or superior thrust and efficiency values to those obtained using two actively controlled degrees of freedom. [Preview Abstract] |
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KP1.00003: Transient Performance of a Vertical Axis Wind Turbine Aykut Onol, Serhat Yesilyurt A coupled CFD/rotor dynamics modeling approach is presented for the analysis of realistic transient behavior of a height-normalized, three-straight-bladed VAWT subject to inertial effects of the rotor and generator load which is manipulated by a feedback control under standardized wind gusts. The model employs the k-$\varepsilon $ turbulence model to approximate unsteady Reynolds-averaged Navier-Stokes equations and is validated with data from field measurements. As distinct from related studies, here, the angular velocity is calculated from the rotor's equation of motion; thus, the dynamic response of the rotor is taken into account. Results include the following: First, the rotor's inertia filters large amplitude oscillations in the wind torque owing to the first-order dynamics. Second, the generator and wind torques differ especially during wind transients subject to the conservation of angular momentum of the rotor. Third, oscillations of the power coefficient exceed the Betz limit temporarily due to the energy storage in the rotor, which acts as a temporary buffer that stores the kinetic energy like a flywheel in short durations. Last, average of transient power coefficients peaks at a smaller tip-speed ratio for wind gusts than steady winds. [Preview Abstract] |
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KP1.00004: Hydrodynamic Disturbances Affect Self-excited Vibrations of Seal Vibrissae . Christin Murphy, William Martin, Aren Hellum, Charles Henoch Seals use their vibrissae, or whiskers, to find prey by hydrodynamic sensing and tracking. As the whiskers move through the water, self-excited vibrations are induced. We hypothesize that the features of these vibrations encode information about the disturbance source. We used laser Doppler vibrometry to study these vibrations in harbor seal whiskers exposed to water flow in a water tunnel with and without an upstream disturbance present, and at various speeds. Whiskers have an elliptical cross-sectional profile, which creates a distinct effect of angle of attack. To examine this effect, experiments were performed with the major axis of the elliptical profile parallel to the flow (0 degrees), and perpendicular to the flow (90 degrees). For the 0 case without a disturbance, the prominent vibration frequency increases as speed increases. When a disturbance is introduced, there is a clear disruption in the prominent vibration frequency. For the 90 case with no disturbance, multiple distinct vibration frequencies are excited. With increase in speed, the relative amplitudes of the excited vibrations change with respect to each other. When a disturbance is introduced, the excited vibration frequencies persist while the energy increases across the computed spectrum. [Preview Abstract] |
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KP1.00005: Experimental investigation of flow-structure interaction between a model biofilm streamer and water flow Farzan Kazemifar, Gianluca Blois, Sumit Sinha, Richard Hardy, James Best, Gregory Sambrook Smith, Kenneth Christensen Biofilms are permeable and deformable material whose bulk structure is composed of extracellular polymeric substance (EPS) that houses bacterial colonies. The EPS is responsible for the mechanical properties of the biofilm. In this study we investigate the fluid-structure interaction between a model biofilm streamer and water flow in a closed-loop water channel in the laminar and transitional flow regimes, using the particle image velocimetry (PIV) technique. The model streamer is fabricated from acrylamide polymer hydrogel. The purpose for using this material is twofold: 1) its mechanical properties (i.e. elastic modulus) can be tuned by controlling its chemical composition, 2) the hydrogel is transparent with a refractive index (RI) very close to that of water, thus minimizing the optical distortions for flow visualization. The velocity vector fields obtained from PIV measurements are used to investigate the temporal evolution of the flow structure in the vicinity of the streamer, focusing on the vortex shedding mechanism and the resulting oscillations of the streamer. [Preview Abstract] |
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KP1.00006: Determining the benefits of Vorticella cell body motion. Matty C. Specht, Rachel E. Pepper Microscopic sessile suspension feeders are single-celled organisms found in aquatic ecosystems. They live attached to underwater surfaces and create a fluid flow in order to feed on bacteria and debris. They participate in the natural degradation of contaminants in water. Understanding the fluid flow they create enhances our knowledge of their environmental impact. One type of suspension feeder, \textit{Vorticella}, have been observed to vary their cell body orientation with respect to their surface, but the benefits of this motion are still unknown. We use simulations to investigate the effect of \textit{Vorticella }body motion on the feeding current and the nutrient flux to the cell body to determine whether or not the motion increases nutrient consumption. We determine the nutrient flux using COMSOL Multiphysics software to solve the advection-diffusion equation with the flow given by a stokeslet model. We use a range of motions similar and dissimilar to that of live \textit{Vorticella}. We find that most patterns of motion do not increase the nutrient flux, since the \textit{Vorticella} feed from regions where they already have depleted the water of nutrients. However, it is possible that their \quad motion could help the \textit{Vorticella }find nutrients that are inhomogenously distributed in water. [Preview Abstract] |
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KP1.00007: Effects of red blood cell deformability on the non-uniform distribution of platelet-sized particles in blood flow through microchannels Masako Sugihara-Seki, Keisuke Sakamoto, Tomoaki Itano, Junji Seki In blood flow through microvessels, platelets are known to have enhanced concentrations near the vessel wall, which is the so-called “near-wall excess (NWE)”. This phenomenon is considered to be caused by the interaction with red blood cells (RBCs); since RBCs have a tendency to approach the vessel centerline due to their highly deformability, they may push away less deformable platelets toward the near-wall region. In order to examine this proposition by in vitro experiments, we measured the distribution of platelet-sized particles mixed in intact RBC or hardened RBC suspensions flowing through microchannels of 50$\mu $m x 50$\mu $m cross-section. Hardened RBCs were prepared by immersing human RBCs in glutaraldehayde solution of 40 -- 4000 ppm. Fluorescent observations were conducted with the use of a confocal laser scanning microscope system with a high-speed video camera. It was found that platelet-sized particles exhibited high concentrations near the channel wall, i.e., NWE, when they were mixed in intact RBC suspensions. By contrast, the particles mixed in hardened RBC suspensions showed weak NWE or uniform distribution over the channel cross-section, indicating that deformability of RBCs plays an essential role in the NWE phenomenon. [Preview Abstract] |
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KP1.00008: On the Normal Force Mechanotransduction of Human Umbilical Vein Endothelial Cells Amir Vahabikashi, Qiuyun Wang, James Wilson, Qianhong Wu In this paper, we report a cellular biomechanics study to examine the normal force mechanotransduction of Human Umbilical Vein Endothelial Cells (HUVECs) with their implications on hypertension. Endothelial cells sense mechanical forces and adjust their structure and function accordingly. The mechanotransduction of normal forces plays a vital role in hypertension due to the higher pressure buildup inside blood vessels. Herein, HUVECs were cultured to full confluency and then exposed to different mechanical loadings using a novel microfluidic flow chamber. One various pressure levels while keeps the shear stress constant inside the flow chamber. Three groups of cells were examined, the control group (neither shear nor normal stresses), the normal pressure group (10 dyne/cm2 of shear stress and 95 mmHg of pressure), and the hypertensive group (10 dyne/cm2 of shear stress and 142 mmHg of pressure). Cellular response characterized by RT-PCR method indicates that, COX-2 expressed under normal pressure but not high pressure; Mn-SOD expressed under both normal and high pressure while this response was stronger for normal pressure; FOS and e-NOS did not respond under any condition. The differential behavior of COX-2 and Mn-SOD in response to changes in pressure, is instrumental for better understanding the pathogenesis of hypertensive cardiovascular diseases. [Preview Abstract] |
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KP1.00009: Investigation of the Left Ventricular Flow Dynamics in the Presence of Severe Mitral Annular Calcification Batoul El - Sayegh, Lyes Kadem, Giuseppe Di Labbio, Gregg S. Pressman, Edinrin Obasare Valvular calcification is frequent with aging and diverse diseases. Mitral annular calcification (MAC) is a degenerative process where the fibrous annulus of the mitral valve degrades. MAC can be found in approximately 40{\%} of people aged over 65. It is associated with increased occurrence of cardiovascular diseases including stroke. This experimental work is aimed to investigate the effects of MAC on the left ventricle (LV) hemodynamics and to develop new clinical parameters. Two patient-specific 3D-printed mitral valves with moderate and severe MACs were placed in a left heart simulator. The velocity fields in the LV were acquired using time-resolved particle image velocimetry (TR-PIV) and compared to normal LV flow. The velocity fields were used to evaluate the temporal evolution of the vorticity fields and viscous energy loss in the LV. The presence of MAC disturbed the flow in the LV leading to markedly increased viscous energy losses. As the severity of MAC increased, the velocity of the inflow jet also increased causing significant perturbations to the normally-occurring vortex in the LV. [Preview Abstract] |
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KP1.00010: Flow Topology in the Right Ventricle after Tetralogy of Fallot Repair Amanda Mikhail, Lyes Kadem, Giuseppe Di Labbio Among all of the known congenital heart defects, Tetralogy of Fallot (TOF) is the most common cyanotic defect, accounting for 5{\%} of all detected defects. Approximately 1 in 2518 births will result with TOF, leading to about 1657 cases per year in the United States$^{\mathrm{\thinspace }}$alone. All of those affected will need surgical repair in order to have a relatively normal life and longer life span. Unfortunately, pulmonary regurgitation (PR) has been observed to appear two to three decades after the initial operation in 50{\%} of operated cases. PR results in abnormal flow patterns in the right ventricle, which are currently poorly understood. In this experimental study, several severities of pulmonary regurgitation were simulated on a newly developed right ventricle using a cardiovascular simulator. The interaction between the tricuspid valve inflow and the pulmonary regurgitation was investigated using Time-resolved particle image velocimetry (TR-PIV). PR resulted in a turbulent jet that disturbed the optimal filling of the RV. Energy losses and viscous shear stresses were observed to significantly increase with the severity of PR. This study can contribute towards a better understanding of the suboptimal performance in patients with repaired TOF. [Preview Abstract] |
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KP1.00011: In vitro evaluation of valve hemodynamics in the pediatric pulmonary outflow tract Nicole Schiavone, Chris Elkins, Doff McElhinney, John Eaton, Alison Marsden Tetraology of Fallot (ToF) is a congenital heart disease that affects 1 in every 2500 newborns each year and requires surgical repair of the right ventricular outflow tract (RVOT) and subsequent placement of an artificial pulmonary valve. While a wide variety of artificial valves are available, essentially all of them become subject to degradation and dysfunction during the patient's lifetime, which leads to additional interventions. However, there is little understanding about the mechanical function of replacement pulmonary valves and no quantitative placement guidelines to ensure maximum failure-free lifetime. This work aims to experimentally assess the biomechanics of pulmonary valves in realistic RVOT geometries using magnetic resonance velocimetry (MRV), which can measure 3D, three-component phase-averaged velocity fields. The RVOT geometries are constructed using 3D printing, allowing for variation in crucial geometric parameters such as the radius of curvature of the main pulmonary artery (MPA) and the dilation of the artery downstream of the valve. A St. Jude Medical Epic valve is secured inside the RVOT geometry and can be interchanged, allowing for variation of the ratio between valve diameter and MPA diameter. This work will discuss the use of MRV to capture the flow structure in the RVOT and evaluate pulmonary valve performance under different conditions. [Preview Abstract] |
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KP1.00012: Intraventricular filling in physical models of the left ventricle: influence of aortic pressure Nicholas Nelsen, Milad Samaee, Arvind Santhanakrishnan Clinical studies using medical imaging have provided evidence on the formation of an intraventricular vortex in the left ventricle (LV) during diastolic phase of the cardiac cycle. However, the question of how the vortex characteristics are altered with aortic pressure remains unclear. This is of relevance to hypertensive heart disease and heart failure with normal ejection fraction. Using an experimental left heart simulator, we have previously shown that increasing LV wall stiffness results in reduction of the filling vortex circulation. In this study, we investigate the effects of varying aortic pressure in addition to wall stiffness. A series of flexible-walled LV models with varying wall stiffness were tested in a pulsatile flow loop. 2D particle image velocimetry was used to visualize intraventricular flow and calculate filling vortex circulation. The flow circuit was first setup with the least stiffness LV physical model, and tuned to physiological aortic pressure, cardiac output and ejection fraction. We then iteratively tested LV models with increasing stiffness without changing circuit variables. Comparisons of the filling vortex circulation with changing aortic pressure relative to the baseline and increased LV stiffness models will be presented. [Preview Abstract] |
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KP1.00013: Effect of the bifurcation angle on the flow within a synthetic model of lower human airways Andres Santiago Espinosa Moreno, Carlos Alberto Duque Daza The effect of the bifurcation angle on the flow pattern developed during respiratory inhalation and exhalation processes was explored numerically using a synthetic model of lower human airways featuring three generations of a dichotomous morphology as described by a Weibel model. Laminar flow simulations were performed for six bifurcation angles and four Reynolds numbers relevant to human respiratory flow. Numerical results of the inhalation process showed a peak displacement trend of the velocity profile towards the inner walls of the model. This displacement exhibited correlation with Dean-type secondary flow patterns, as well as with the onset and location of vortices. High wall shear stress regions on the inner walls were observed for a range of bifurcation angles. Noteworthy, specific bifurcation angles produced higher values of pressure drop, compared to the average behavior, as well as changes in the volumetric flow through the branches. Results of the simulations for exhalation process showed a different picture, mainly the appearance of symmetrical velocity profiles and the change of location of the regions of high wall shear stress. The use of this modelling methodology for biomedical applications is discussed considering the validity of the obtained results. [Preview Abstract] |
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KP1.00014: Large Eddy Simulation of “turbulent-like” flow in intracranial aneurysms Muhammad Owais Khan, Christophe Chnafa, David A. Steinman, Simon Mendez, Franck Nicoud Hemodynamic forces are thought to contribute to pathogenesis and rupture of intracranial aneurysms (IA). Recent high-resolution patient-specific computational fluid dynamics (CFD) simulations have highlighted the presence of “turbulent-like” flow features, characterized by transient high-frequency flow instabilities. In-vitro studies have shown that such “turbulent-like” flows can lead to lack of endothelial cell orientation and cell depletion, and thus, may also have relevance to IA rupture risk assessment. From a modelling perspective, previous studies have relied on DNS to resolve the small-scale structures in these flows. While accurate, DNS is clinically infeasible due to high computational cost and long simulation times. In this study, we present the applicability of LES for IAs using a LES/blood flow dedicated solver (YALES2BIO) and compare against respective DNS. As a qualitative analysis, we compute time-averaged WSS and OSI maps, as well as, novel frequency-based WSS indices. As a quantitative analysis, we show the differences in POD eigenspectra for LES vs. DNS and wavelet analysis of intra-saccular velocity traces. Differences in two SGS models (i.e. Dynamic Smagorinsky vs. Sigma) are also compared against DNS, and computational gains of LES are discussed. [Preview Abstract] |
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KP1.00015: A critical velocity of squeezing a droplet through a circular constriction: implications on ischemic stroke Zhifeng Zhang, Corina Drapaca Ischemic stroke accounts for about 87 percent of all stroke cases. In these cases, models of squeezing a droplet through a smaller constriction channel can help better understand the pathology and capillary restoring after a Stroke. In the present research, we analytical expressed the minimum impulse of squeezing a droplet through a circular channel as well as its critical velocity. By comparison with a previously defined critical velocity, we find the difference between these two. Applications of this research in the understanding of ischemic stroke are also discussed. [Preview Abstract] |
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KP1.00016: Swimming performance of biomimetic trapezoidal elastic fins Michael Spadaro, Peter Yeh, Alexander Alexeev Using three-dimensional computer simulations, we probe the biomimetic free-swimming of trapezoidal elastic plates plunging sinusoidally in a viscous fluid, varying the frequency of oscillations and plate geometry. We choose the elastic trapezoidal plate geometry because it more closely approximates the shape of real caudal fish fins. Indeed, caudal fins are found in nature in a variety of trapezoidal shapes with different aspect ratios. Because of this, we perform our simulations using plates with aspect ratios varying from the cases where the plate has a longer leading edge and to plates with a longer trailing edge. We find that the trapezoidal fins with the longer trailing edge are less efficient than the rectangular fins at the equivalent oscillation frequencies. This is surprising because many fish found in nature have a widening tail. We relate this to the fact that our model considers fins with uniform thickness whereas fish uses tapered fins. Our results will be useful for the design of biomimetic swimming devices as well as understanding more closely the physics of fish swimming. [Preview Abstract] |
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KP1.00017: Mechanical krill models for studying coordinated swimming Alice Montague, Hong Kuan Lai, Milad Samaee, Arvind Santhanakrishnan The global biomass of Homo sapiens is about a third of the biomass of Euphausia superba, commonly known as the Antarctic krill. Krill participate in organized social behavior. Propulsive jets generated by individual krill in a school have been suggested to be important in providing hydrodynamic sensory cues. The importance of body positions and body angles on the wakes generated is challenging to study in free swimming krill. Our solution to study the flow fields of multiple krill was to develop mechanical krill robots. We designed krillbots using mostly 3D printed parts that are actuated by stepper motors. The krillbot limb lengths, angles, inter-limb spacing and pleopod stroke frequency were dynamically scaled using published data on free-swimming krill kinematics. The vertical and horizontal spacing between krillbots, as well as the body angle, are adjustable. In this study, we conducted particle image velocimetry (PIV) measurements with two tethered krillbots in a flow tank with no background flow. One krillbot was placed above and behind the other. Both krillbots were at a zero-degree body angle. Wake-body interactions visualized from PIV data will be presented. [Preview Abstract] |
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KP1.00018: Impact of Morphological Changes on the Motility of {\it Amoeba proteus} Sunitha Shroff N Bio-mechanical properties of cell membrane, actin and cytoskeleton have influence on the cell locomotion. To explore, morphological changes were induced in {\it Amoeba proteus} by depriving nutrition, also either through ATP mediated or through KCl mediated membrane depolarization. We observed that, membrane depolarization leads to complete loss/reduction of pseudopodia in a dose dependent manner, gradually {\it A. proteus} becomes globular. We also report that with depravation of its nutrition (Chilomonas) {\it A. proteus} transforms them into tube/filament like structure and this transformation is reversible with the supply of Chilomonas. Results indicate that the structural and locomotion variation of {\it A. proteus} through nucleotides may not be just a membrane phenomenon, but may involve signaling mechanisms. Further, we carried out immunostaining of {\it A. proteus} with P2X2 and P2Y2 antibodies to analyze their localization and the extent of expression. The result indicated that in normal {\it A. proteus} receptors are dispersed uniformly, whereas in filament shaped {\it A. proteus} P2X2-receptor was found to be localized, unlike P2Y2 receptor. As nucleotides are known to cause structural changes in the organism, we report corresponding changes in their locomotion. [Preview Abstract] |
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KP1.00019: Financial Assets [ share, bonds ] {\&} Ancylia WH- Maksoed Instead Elaine Scarry: \textbf{``Thermonuclear monarchy'' }reinvent Carry Nation since Aug 17, 1965 the Republic of Indonesia's President speech: \textbf{``Reach to the Star'' }, for \textit{``cancellation'' }usually found in External Debt herewith retrieved from ``the Window of theWorld'': \textit{Ancylia }, feast in March, a month named after Mars, the god of war. ``On March 19 they used to put on their biggest performance of gymnastics in order to ``bribe'' their god for another good year'', further we have vacancy {\&} ``vacuum tube''- Bulat Air karena Pembuluh, Bulat Kata karena Mufakat'' proverb from Minangkabau, West Sumatra. Follows March 19, 1984 are first prototype flight of IAI Astra Jet as well as March 19, 2012 invoice accompanies Electric car Kujang-193, Fainancial Assets [share, bonds] are the answer for ``infrastructure'' {\&} state owned enterprises assets to be hedged first initial debt per capita accordances. [Preview Abstract] |
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KP1.00020: Numerical simulation of ultrasound-induced dynamics of a gas bubble neighboring a rigid wall Tatsuya Kobayashi, Keita Ando Cavitation erosion has been a technical issue in ultrasonic cleaning under which cavitation bubbles appear near target surfaces to be cleaned. In the present study, we numerically study the interaction of ultrasonic standing waves with a gas bubble in the neighborhood of a rigid wall. We solve multicomponent Euler equations that ignore surface tension and phase change at interfaces, by the finite-volume WENO scheme with interface capturing. The pressure amplitude of the ultrasound is set at several atmospheres and the ultrasound wavelength is tuned to obtain the situation near resonance. In the simulation, we observe jetting flow toward the rigid wall at violent bubble collapse that may explain cavitation erosion in ultrasonic cleaning. [Preview Abstract] |
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KP1.00021: Investigating short-time dynamics of spreading bubbles Matthieu Laurent, Mark Menesses, James Bird When a bubble comes into contact with a partially wetting surface, the film between the bubble and solid surface rapidly dewets to minimize the free energy of the system. The dynamics of this dewetting is assumed to be dominated by capillary and viscous effects. Yet, when drops rather than bubbles spread, the short-time dynamics are dominated by a balance of capillarity and inertia. Here we revisit spreading bubbles to investigate whether the short-time dynamics is better captured by a viscous or inertial scaling. Counter-intuitively, neither viscous nor inertial effects alone can account for short-time spreading dynamics. Through an experimental approach, we develop a dimensionless scaling relation --- incorporating both viscosity and inertia --- that successfully collapses the data. [Preview Abstract] |
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KP1.00022: High-speed visualization and radiated pressure measurement of a laser-induced gas bubble in glycerin-water solutions Takehiro Nakajima, Tomoki Kondo, Keita Ando We study the dynamics of a spherical gaseous bubble created by focusing a nanosecond laser pulse at 532 nm into a large volume of glycerin-water solutions. Free oscillation of the bubble and shock wave emission from the bubble dynamics are recorded by a high-speed camera together with a pulse laser stroboscope; concurrently, pressure radiated from the oscillating bubble is measured by a hydrophone. The bubble achieves a mechanical equilibrium after free oscillation is damped out; the equilibrium state stays for a while, unlike vapor bubbles. We speculate that the bubble content is mainly gases originally dissolved in the liquid (i.e., air). The bubble dynamics we observed are compared to Rayleigh-Plesset-type calculations that account for diffusive effects; the (unknown) initial pressure just after laser focusing is tuned to obtain agreement between the experiment and the calculation. Moreover, viscous effects on the shock propagation are examined with the aid of compressible Navier-Stokes simulation. [Preview Abstract] |
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KP1.00023: Diffusion-driven growth of a spherical gas bubble in gelatin gels supersaturated with air Eriko Shirota, Keita Ando We experimentally and theoretically study diffusion-driven growth of laser-induced gas bubbles in gelatin gels supersaturated with air. The supersaturation in the gels is realized by using a large separation between heat and mass diffusion rates. An optical system is developed to induce bubble nucleation by laser focusing and visualize the subsequent bubble growth. To evaluate the effect of the gel elasticity on the bubble growth rate, we propose the extended Epstein-Plesset theory that considers bubble pressure modifications due to linear/nonlinear elasticity (in addition to Laplace pressure). From comparisons between the experiments and the proposed theory, the bubble growth rate is found to be hindered by the elasticity. [Preview Abstract] |
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KP1.00024: Epstein-Plesset theory based measurements of concentration of nitrogen gases dissolved in aerated water Masashi Sasaki, Tatsuya Yamashita, Keita Ando Microbubble aeration is used to dissolved gases into water and is an important technique in agriculture and industry. We can measure concentration of dissolved oxygen (DO) in aerated water by commercial DO meters. However, there do not exist commercially available techniques to measure concentration to dissolved nitrogen (DN). In the present study, we propose the method to measure DN in aerated water with the aid of Epstein-Plesset-type analysis. Gas-supersaturated tap water is produced by applying aeration with micro-sized air bubbles and is then stored in a glass container open to the atmosphere. Diffusion-driven growth of bubbles nucleated at the container surface is recorded with a video camera. The bubble growth rate is compare to the extended Epstein-Plesset theory that models mass transfer of both DO and DN into the surface-attached bubbles base on the diffusion equation. Given the DO measurements, we can obtain the DN level by fitting in the comparison. [Preview Abstract] |
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KP1.00025: Shock Refraction at Semi-Rigid Interfaces Gabrielle Miller, James Reynolds We consider a strong spherical air shock encountering a planar interface separating the air from a medium of significantly higher impedance, with the goal of obtaining an approximate analytic description. Before encountering the interface, the incident air shock is well described by the Taylor-Sedov solution for a point blast. The behavior of the reflected and transmitted shocks differs depending upon the height of burst. For moderate heights, despite the relatively small amount of energy transferred, the pressure in the second medium may be much higher than that behind the air shock due to the strong impedance mismatch [1]. Near-surface blasts may be further complicated by the entrainment of material from the second medium and/or the deflection of the interface caused by the strong air shock. For the present study, we ignore the effects of entrainment and assume that the deformation of the interface is small compared to the height of burst. We then investigate the relationship between energy loss into the second medium and the reflected air shock. [1] L. Henderson, M. Jia-Huan, S. Akira, T. Kazuyoshi, Fluid Dynamics Research \textbf{5}(5-6), 337 (1990) [Preview Abstract] |
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KP1.00026: Inclusion of Separation in Integral Boundary Layer Methods Brodie Wallace, Charles O'Neill An integral boundary layer (IBL) method coupled with a potential flow solver quickly allows simulating aerodynamic flows, allowing for aircraft geometries to be rapidly designed and optimized. However, most current IBL methods lack the ability to accurately model three-dimensional separated flows. Various IBL equations and closure relations were investigated in an effort to develop an IBL capable of modeling separation. Solution techniques, including a Newton's method and the inverse matrix solving program GMRES, as well as methods for coupling an IBL with a potential flow solver were also investigated. Results for two-dimensional attached flow as well as methods for expanding an IBL to model three-dimensional separation are presented. [Preview Abstract] |
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KP1.00027: Validation of Magnetic Resonance Thermometry by Computational Fluid Dynamics Grant Rydquist, Mark Owkes, Claire M. VerHulst, Michael J. Benson, Bret P. VanPoppel, Sascha Burton, John K. Eaton, Christopher P. Elkins Magnetic Resonance Thermometry (MRT) is a new experimental technique that can create fully three-dimensional temperature fields in a noninvasive manner. However, validation is still required to determine the accuracy of measured results. One method of examination is to compare data gathered experimentally to data computed with computational fluid dynamics (CFD). In this study, large-eddy simulations have been performed with the NGA computational platform to generate data for a comparison with previously run MRT experiments. The experimental setup consisted of a heated jet inclined at 30\textdegree injected into a larger channel. In the simulations, viscosity and density were scaled according to the local temperature to account for differences in buoyant and viscous forces. A mesh-independent study was performed with 5 mil-, 15 mil- and 45 mil-cell meshes. The program Star-CCM$+$ was used to simulate the complete experimental geometry. This was compared to data generated from NGA. Overall, both programs show good agreement with the experimental data gathered with MRT. With this data, the validity of MRT as a diagnostic tool has been shown and the tool can be used to further our understanding of a range of flows with non-trivial temperature distributions. [Preview Abstract] |
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KP1.00028: Statistical Inference of a RANS closure for a Jet-in-Crossflow simulation Jan Heyse, Wouter Edeling, Gianluca Iaccarino The jet-in-crossflow is found in several engineering applications, such as discrete film cooling for turbine blades, where a coolant injected through hols in the blade's surface protects the component from the hot gases leaving the combustion chamber. Experimental measurements using MRI techniques have been completed for a single hole injection into a turbulent crossflow, providing full 3D averaged velocity field. For such flows of engineering interest, Reynolds-Averaged Navier-Stokes (RANS) turbulence closure models are often the only viable computational option. However, RANS models are known to provide poor predictions in the region close to the injection point. Since these models are calibrated on simple canonical flow problems, the obtained closure coefficient estimates are unlikely to extrapolate well to more complex flows. We will therefore calibrate the parameters of a RANS model using statistical inference techniques informed by the experimental jet-in-crossflow data. The obtained probabilistic parameter estimates can in turn be used to compute flow fields with quantified uncertainty. [Preview Abstract] |
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KP1.00029: A numerical study of natural convection in eccentric spherical annuli Angel Gallegos, Carlos Malaga A fluid between two spheres, concentric or not, at different temperatures will flow in the presence of a constant gravitational force. Although there is no possible hydrostatic state, energy transport is dominated by diffusion if temperature difference between the spheres is small enough. By the use of a full three-dimensional thermal lattice Boltzmann model we study the transition between the conductive, the steady convective, and the unsteady convective regimes. We use the concentric case to validate the results by comparing with experiments and numerical simulations found in the literature, and then we extend our numerical experiments to the eccentric case to observe the general behavior of the different regimes. We analyze the energy transport characterized by the relation between Nusselt and Rayleigh numbers as well as the arising flow patterns. [Preview Abstract] |
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KP1.00030: ABSTRACT WITHDRAWN |
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KP1.00031: The effect of temperature on the impact process of SiO$_{\mathrm{2}}$ particle onto a planar surface Ming Dong, Sufen Li, Yan Shang This paper presents the results of a comprehensive program of experiments in which SiO$_{\mathrm{2}}$ particles were impacted under controlled conditions against a planar steel surface. The overall aim of these experiments was to gain an understanding of the ash deposition process in a pulverized coal boiler system. A continuous nitrogen flow carrying particles was used to simulate the flue gas in boiler, and planer steel surface was used to simulate the heat transfer tube in boiler. The effect of particle incident velocity, particle temperature and planar surface temperature on the normal restitution coefficient was examined. The results show that the normal restitution coefficient increases firstly with increasing incident velocity, and then decreases with increasing incident velocity in the measurement range (ranging from 8m/s to 13m/s). The normal restitution coefficient decreases with increasing particle temperature and surface temperature, and with temperature difference between particle and surface. The experiments are carried out in an atmospheric column, and individual impacts are recorded by a digital camera system. Keywords: Normal restitution coefficient, impaction experiments, particle, rebound characteristics. [Preview Abstract] |
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KP1.00032: Peruvian perovskite Between Transition-metal to PGM/PlatinumGroupMetal Catalytic Fusion WH- Maksoed Strongly correlated electronic materials made of simple building blocks, such as a transition-metal ion in an octahedral oxygen cage forming a perovskite structure- Dagotto {\&} Tokura for examples are the high-temperature superconductivity {\&} the CMR/Colossal Magnetoresistance . Helium-4 denotes from LC Case,ScD: \textbf{``Catalytic Fusion of Deuterium into Helium-4''}- 1998 dealt with gaseous D$_{\mathrm{2\thinspace }}$-- ``contacted with a supported metallic catalyst at superatmospheric pressure''. The catalyst is a platinum-group metal, at about 0.5 {\%} - 1 {\%} by weight, on activated C. Accompanies Stephen J Geier, 2010 quotes ``transition metal complexes'', the Energy thus produced is enormous, and because the deuterium is very cheap in the form of heavy water (less than US {\$} 1/g ), the fuel cost is very low ( \textless \textless 1 {\%}/KwH ). ``The oceans contain enough deuterium to satisfy the Earth's energy needs for many millions of year'' to keep ``maria''/Latin name of seas {\&}Deuteronomy to be eternally preserves. [Preview Abstract] |
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KP1.00033: Design Considerations of a Solid State Thermal Energy Storage Mohammad Janbozorgi, Sammy Houssainy, Ariana Thacker, Peggy Ip, Walid Ismail, Pirouz Kavehpour With the growing governmental restrictions on carbon emission, renewable energies are becoming more prevalent. A reliable use of a renewable source however requires a built-in storage to overcome the inherent intermittent nature of the available energy. Thermal design of a solid state energy storage has been investigated for optimal performance. The impact of flow regime, laminar vs. turbulent, on the design and sizing of the system is also studied. The implications of low thermal conductivity of the storage material are discussed and a design that maximizes the round trip efficiency is presented. [Preview Abstract] |
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KP1.00034: Ghost Particle Velocimetry implementation in millimeters devices and comparison with $\mu$PIV Marco Riccomi, Federico Alberini, Elisabetta Brunazzi, Daniele Vigolo Micro/milli-fluidic devices are becoming an important reference for several disciplines and are quickly increasing their applications in scientific, as well as industrial, environment. As a consequence, the development of techniques able to analyse these kinds of systems is required to allow their progress. Here we show the implementation of the Ghost Particle Velocimetry (GPV) for the flow velocity field investigation in milli-fluidic devices. This innovative technique has been recently introduced, and has been already proven to be useful in describing rapid phenomenon at a small scale. In this work, the GPV has been used to characterize the trapping of light suspended material in a branching junction. Experiments have been performed to identify the flow velocity field close to a millimeters scale T-junction, at different Reynolds numbers. Particularly interesting are the complex structures, such as vortices and recirculation zones, induced by the vortex breakdown phenomenon. The results obtained have been deeply validated and compared with the well-established $\mu$PIV, highlighting the differences in terms of qualitative and quantitative parameters. A performance comparison has been designed to underline the strengths and weaknesses of the two experimental techniques. [Preview Abstract] |
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KP1.00035: Capillary rise in crumped-sheets of paper Ayax Hernando Torres Victoria, Moisés Salgado, Salomón Peralta, Franciso Wong, Abraham Medina In this work we report experiments on the capillary rise of water into crumpled paper, in order to understand how the controlled damage of a soft material, like paper (hand-crumpled paper sheets), improves their capabilities of liquid sorption. We have done a series of experiments where a different number of crumples (from zero up to fifty) were made on different rectangular paper pieces and we found that an increasing number of crumples enhances such a capability. Characteristic power laws for the front of elevation, h, versus the elapsed time to reach such height, t, are reported. [Preview Abstract] |
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KP1.00036: Effect of Viscosity on Liquid Curtain Stability Alireza Mohammad Karim, Wieslaw Suszynski, Lorraine Francis, Marcio Carvalho The effect of viscosity on the stability of Newtonian liquid curtains was explored by high-speed visualization. Glycerol/water solutions with viscosity ranging from 19.1 to 210 mPa.s were used as coating liquids. The experimental set-up used a slide die delivery and steel tube edge guides. The velocity along curtain at different positions was measured by tracking small particles at different flow conditions. The measurements revealed that away from edge guides, velocity is well described by free fall effect. However, close to edge guides, liquid moves slower, revealing formation of a viscous boundary layer. The size of boundary layer and velocity near edge guides are strong function of viscosity. The critical condition was determined by examining flow rate below which curtain broke. Curtain failure was initiated by growth of a hole within liquid curtain, close to edge guides. Visualization results showed that the hole forms in a circular shape then becomes elliptical as it grows faster in vertical direction compared to horizontal direction. As viscosity rises, minimum flow rate for destabilization of curtain increased, indicating connection between interaction with edge guides and curtain stability. [Preview Abstract] |
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KP1.00037: Flow and Acoustic Features of a Mach 0.9 Free Jet Using High-Frequency Excitation Puja Upadhyay, Farrukh Alvi This study focuses on active control of a Mach 0.9 ($Re_D=6\times10^5$) free jet using high-frequency excitation for noise reduction. Eight resonance-enhanced microjet actuators with nominal frequencies of 25 kHz ($St_{D}\approx2.2$) are used to excite the shear layer at frequencies that are approximately an order of magnitude higher than the jet preferred frequency. The influence of control on mean and turbulent characteristics of the jet is studied using Particle Image Velocimetry. Additionally, far-field acoustic measurements are acquired to estimate the effect of pulsed injection on noise characteristics of the jet. Flow field measurements revealed that strong streamwise vortex pairs, formed as a result of control, result in a significantly thicker initial shear layer. This excited shear layer is also prominently undulated, resulting in a modified initial velocity profile. Also, the distribution of turbulent kinetic energy revealed that forcing results in increased turbulence levels for near-injection regions, followed by a global reduction for all downstream locations. Far-field acoustic measurements showed noise reductions at low to moderate frequencies. Additionally, an increase in high-frequency noise, mostly dominated by the actuators’ resonant noise, was observed. [Preview Abstract] |
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KP1.00038: Effect of noise on Rayleigh-Taylor mixing with time-dependent acceleration Nora Swisher, Arun Pandian, Snezhana Abarzhi We perform a detailed stochastic study of Rayleigh-Taylor (RT) mixing with time-dependent acceleration. A set of nonlinear stochastic differential equations with multiplicative noise is derived on the basis of momentum model and group theory analysis. A broad range of parameters is investigated, and self-similar asymptotic solutions are found. The existence is shown of two sub-regimes of RT mixing dynamics – the acceleration-driven and the dissipation-driven mixing. In each sub-regime, statistic properties of the solutions are investigated, and dynamic invariants are found. Transition between the sub-regimes is studied. [Preview Abstract] |
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KP1.00039: Effect of pressure fluctuations on Richtmyer-Meshkov coherent structures Aklant K. Bhowmick, Snezhana Abarzhi We investigate the formation and evolution of Richtmyer Meshkov bubbles after the passage of a shock wave across a two fluid interface in the presence of pressure fluctuations. The fluids are ideal and incompressible and the pressure fluctuations are scale invariant in space and time, and are modeled by a power law time dependent acceleration field with exponent -2. Solutions indicate sensitivity to pressure fluctuations. In the linear regime, the growth of curvature and bubble velocity is linear. The growth rate is dominated by the initial velocity for weak pressure fluctuations, and by the acceleration term for strong pressure fluctuations. In the non-linear regime, the bubble curvature is constant and the solutions form a one parameter family (parametrized by the bubble curvature). The solutions are shown to be convergent and asymptotically stable. The physical solution (stable fastest growing) is a flat bubble for small pressure fluctuations and a curved bubble for large pressure fluctuations. The velocity field (in the frame of references accounting for the background motion) involves intense motion of the fluids in a vicinity of the interface, effectively no motion of the fluids away from the interfaces, and formation of vortical structures at the interface. [Preview Abstract] |
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KP1.00040: Dimensional crossover in Richtmyer-Meshkov unstable flows in the presence of pressure fluctuations Aklant K. Bhowmick, Snezhana Abarzhi We analyze Richtmyer-Meshkov unstable interfacial dynamics in the presence of pressure fluctuations. The pressure fluctuations are scale invariant and are modeled by an effective time dependent acceleration field with power law exponent -2. The group theory based analysis is applied to 3D rectangular p2mm, 3D square p4mm and 2D pm1 RM flows. From the symmetry analysis, we find that 3D square and 2D bubbles form a one parameter family and 3D rectangular bubbles form a two parameter family. The families are parametrized by the principal curvature(s). The bubble velocity and Fourier amplitude profiles exhibit RM type behavior for weak accelerations and RT type behavior for strong accelerations. Under the dimensional crossover, the bubbles elongated in one of the directions reduce to the 2D solutions, whereas the bubbles elongated in the other direction flatten. Stability analysis shows that 3D square bubbles are stable with respect to isotropic as well as anisotropic perturbations. 2D bubbles are unstable to 3D perturbations. No continuous transition is possible between 3D square and 2D bubbles and the dimensional crossover is discontinuous for both strong and weak pressure fluctuations. [Preview Abstract] |
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KP1.00041: Experiments and simulations of Richtmyer-Meshkov Instability with measured,volumetric initial conditions. Everest Sewell, Kevin Ferguson, Jeffrey Jacobs, Jeff Greenough, Vitaliy Krivets We describe experiments of single-shock Richtmyer-Meskhov Instability (RMI) performed on the shock tube apparatus at the University of Arizona in which the initial conditions are volumetrically imaged prior to shock wave arrival. Initial perturbations play a major role in the evolution of RMI, and previous experimental efforts only capture a single plane of the initial condition. The method presented uses a rastered laser sheet to capture additional images throughout the depth of the initial condition immediately before the shock arrival time. These images are then used to reconstruct a volumetric approximation of the experimental perturbation. Analysis of the initial perturbations is performed, and then used as initial conditions in simulations using the hydrodynamics code ARES, developed at Lawrence Livermore National Laboratory (LLNL). Experiments are presented and comparisons are made with simulation results. [Preview Abstract] |
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KP1.00042: Design and Construction of a Shock Tube Experiment for Multiphase Instability Experiments John Middlebrooks, Wolfgang Black, Constantine Avgoustopoulos, Roy Allen, Raj Kathakapa, Qiwen Guo, Jacob McFarland Hydrodynamic instabilities are important phenomena that have a wide range of practical applications in engineering and physics. One such instability, the shock driven multiphase instability (SDMI), arises when a shockwave accelerates an interface between two particle-gas mixtures with differing multiphase properties. The SDMI is present in high energy explosives, scramjets, and supernovae. A practical way of studying shock wave driven instabilities is through experimentation in a shock tube laboratory. This poster presentation will cover the design and data acquisition process of the University of Missouri's Fluid Mixing Shock Tube Laboratory. In the shock tube, a pressure generated shockwave is passed through a multiphase interface, creating the SDMI instability. This can be photographed for observation using high speed cameras, lasers, and advance imaging techniques. Important experimental parameters such as internal pressure and temperature, and mass flow rates of gases can be set and recorded by remotely controlled devices. The experimental facility provides the University of Missouri's Fluid Mixing Shock Tube Laboratory with the ability to validate simulated experiments and to conduct further inquiry into the field of shock driven multiphase hydrodynamic instabilities. [Preview Abstract] |
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KP1.00043: The effect of confinement length on the stability of planar dense wakes Minqiang Si, Vikrant Gupta, Larry K.B. Li Planar dense wakes can be found in many industrial processes, such as combustion and paper-making. Confinement is known to make such wakes more locally absolutely unstable,\footnote{Juniper, M.P. 2006 \textbf{J. Fluid Mech.} 565, 171--195.} but this destabilizing effect has not been comprehensively examined in real wakes bounded by a finite streamwise domain. For example, it is not known (i) how long the confinement walls should be and (ii) what the critical values of the operating parameters should be for global instability to occur. In this experimental study, we try to answer these questions by examining a planar dense wake consisting of a central stream of CO$_2$ (dense gas) sandwiched by two identical outer streams of air (light gas). The wake is confined by solid walls of variable length, which act as an adjustable confinement. We find that the confinement length has a strong influence on the hydrodynamic stability of the wake: (a) self-excited global oscillations appear only when the confinement length exceeds a critical value and (b) the streamwise location of the wavemaker changes with confinement length. Knowledge of how long the confinement walls should be for global instability to occur under various conditions could be useful for optimizing industrial processes. [Preview Abstract] |
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KP1.00044: Mobility functions of a spheroidal particle near a planar elastic membrane Abdallah Daddi-Moussa-Ider, Maciej Lisicki, Stephan Gekle Using an analytical theory, we compute the leading order corrections to the translational, rotational and translation-rotation coupling mobilities of a prolate spheroid immersed in a Newtonian fluid and moving nearby an elastic cell membrane. The corrections are expressed in terms of the spheroid-to-membrane distance, spheroid orientation and the characteristic frequencies associated with membrane shearing and bending. We find that the corrections to the translation-rotation coupling mobility are primarily determined by bending resistance whereas shearing elasticity manifests itself in a more pronounced way in the rotational mobility. We further demonstrate the validity of the analytical approximation by close comparison with boundary integral simulations of a truly extended spheroidal particle. The analytical calculations are found to be in a good agreement with the numerical simulations over the whole range of the applied frequencies. [Preview Abstract] |
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KP1.00045: Three Dimensional Plenoptic PIV Measurements of a Turbulent Boundary Layer Overlying a Hemispherical Roughness Element Kyle Johnson, Brian Thurow, Taehoon Kim, Gianluca Blois, Kenneth Christensen Three-dimensional, three-component (3D-3C) measurements were made using a plenoptic camera on the flow around a roughness element immersed in a turbulent boundary layer. A refractive index matched approach allowed whole-field optical access from a single camera to a measurement volume that includes transparent solid geometries. In particular, this experiment measures the flow over a single hemispherical roughness element made of acrylic and immersed in a working fluid consisting of Sodium Iodide solution. Our results demonstrate that plenoptic particle image velocimetry (PIV) is a viable technique to obtaining statistically-significant volumetric velocity measurements even in a complex separated flow. The boundary layer to roughness height-ratio of the flow was 4.97 and the Reynolds number (based on roughness height) was 4.57\texttimes 10$^{\mathrm{3}}$. Our measurements reveal key flow features such as spiraling legs of the shear layer, a recirculation region, and shed arch vortices. Proper orthogonal decomposition (POD) analysis was applied to the instantaneous velocity and vorticity data to extract these features. [Preview Abstract] |
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KP1.00046: Experimental Gravity Currents Propagating Downslope Over A Synthetic Topography Andrea Burgos Cuevas, Angel Ruiz-Angulo, Carlos Palacios-Morales Lock-release gravity currents are studied experimentally in order to investigate their dynamics and the mixing process between them and the ambient fluid. We produced these currents in a laboratory tank and allow them to propagate downslope first in a flat slope and then in a rough one with a synthetic topography. This topography is similar to the one of a side of a mountain near mexico's valley. Our aim is to investigate the dynamics of gravity currents as similar as possible to the mountain breezes that can develop around this valley. To the best of our knowledge, there are few experimental investigations that take into account the roughness of the slope. For each experiment, we obtain the instantaneous velocity fields using the standard piv technique. From the velocity fields, we estimate the entrainment coefficient time series. We found that this coefficient depends on the roughness of the surface where the current propagates. Besides, pressure time series were obtained in synthetic stations along the rough profile. These series showed a very clear signal of the gravity current propagating along the slope. [Preview Abstract] |
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KP1.00047: Oceanic Double-Diffusive Layer Thicknesses in the Presence of Turbulence Nicole Shibley, Mary-Louise Timmermans Double-diffusive stratification in the ocean is characterized by staircase structures consisting of mixed layers separated by high-gradient interfaces in temperature and salinity. Several past studies have examined mechanisms that govern the observed thicknesses of staircase mixed layers. In one formalism, the mixed-layer thickness is set by layer formation that arises when a heat source is applied at the base of water that is stably-stratified in salinity; in another, the equilibrium thickness of mixed layers has been explained as the product of ``merging,'' where thin layers continue to grow until they reach a thickness determined by a criterion relating the ratio of heat flux to salt flux and the density ratio. We extend the above two theories to consider the influence of turbulence on mixed-layer thicknesses. The study has implications for the Arctic Ocean where double-diffusive staircases are widely present, and mixed-layer thicknesses are well-resolved by ocean measurements. Our theoretical framework provides a means to determine turbulent diffusivities (in regions where microstructure measurements are not available) by considering only observations of density ratio, stratification, and layer thicknesses. [Preview Abstract] |
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KP1.00048: The relationship between double-diffusive intrusions and staircases in the Arctic Ocean Yana Bebieva, Mary-Louise Timmermans The origin of double-diffusive staircases in the Arctic Ocean is investigated for the particular background setting in which both temperature and salinity increase with depth. Motivated by observations that show the co-existence of thermohaline intrusions and double-diffusive staircases, a linear stability analysis is performed on the governing equations to determine the conditions under which staircases form. It is shown that a double-diffusive staircase can result from interleaving motions if the observed bulk vertical density ratio is below a critical vertical density ratio estimated for particular lateral and vertical background temperature and salinity gradients. Vertical temperature and salinity gradients dominate over horizontal gradients in determining whether staircases form. Examination of Arctic Ocean temperature and salinity measurements indicates that observations are consistent with the theory for reasonable choices of eddy diffusivity and viscosity. [Preview Abstract] |
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KP1.00049: Shock Instability and Pattern Emergence in Oscillated Granular Media Justin Stuck, Sarah Anderson, Barbara Skrzypek, Jon Bougie We study shocks formed in vertically oscillated layers of granular media and how shock instability relates to resultant pattern formation. Layers of granular media oscillated vertically on a plate at accelerational amplitudes greater than gravity are tossed off the plate, and shocks are formed upon the layers’ return to the plate. Previous studies have shown that the emergence of standing-wave patterns is dependent on the plate’s accelerational amplitude and oscillation frequency. We numerically solve continuum equations to Navier-Stokes order using forward-time, centered space (FTCS) differencing on a three-dimensional spatial grid. We employ variable timesteps and parallelization for efficiency. These simulations demonstrate shock instability before and after the onset of patterns. We use data from these simulations to investigate the connection between shock instability and pattern emergence. [Preview Abstract] |
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KP1.00050: Oscillation Frequency and Pattern Wavelength in Shaken Granular Media Sarah Anderson, Barbara Skrzypek, Justin Stuck, Jon Bougie When a layer of grains atop a plate is vertically oscillated at amplitudes greater than that of gravity, the layer of the material leaves the plate at some point in the cycle. Shocks form in the layer upon its return collision with the plate. Standing wave patterns also form at various amplitudes exceeding a critical value for the system. Previous research has examined the relationship between the shock strength and driving frequency at a fixed layer depth and accelerational amplitude. For a given layer depth, a decrease in frequency corresponds to a stronger shock and greater pattern wavelength. We characterize the base state of the system by investigating the shocks just prior to pattern formation in the media, using numerical simulations of continuum equations to Navier-Stokes order. We use this characterization to study the relationship between shock instability and the patterns formed in these layers. [Preview Abstract] |
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KP1.00051: Magnetohydrodynamic simulations of a magnetized spherical couette experiment Elliot Kaplan, Henri-Claude Nataf, Nathanael Schaeffer Magnetized spherical Couette flow is a common test bed for studying astro- and geophysically relevant magnetohydrodynamics. A magnetic field is applied to an electrically conductive fluid lying between two co- or counterrotating spheres, and the flow and the magnetic fields influence each other in subtle or dramatic ways. One such experiment, the Derviche Tourneur Sodium experiment (DTS-$\Omega$) recently went through a set of upgrades to better characterize the flows and induced magnetic fields. In tandem with the upgrades, a set of direct numerical simulations were run with the XSHELLS code to give a more complete view of the fluid and magnetic dynamics at various rotation rates of the inner and outer spheres. XSHELLS is a highly efficient hybrid finite-diference pseudospectral solver of the coupled Navier-Stokes and magnetic induction equations. These simulations reveal several dynamic regimes determined by the Rossby number $(Ro = \Delta \Omega / \Omega_o)$. These include quasigeostrophic flows, saturated hydrodynamic instabilities, and long lived filamentary structures. By comparing the high spatial resolution measurements of the simulation with the long duration measurements of the experiment, we can get a more complete picture of the dynamic system we're exploring. [Preview Abstract] |
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KP1.00052: Thermoelectrokinetic instability in micro/nanoscales Georgy Ganchenko, Natalia Ganchenko A novel sophisticated type of electro-hydrodynamic instability in an electrolyte solution near ion-selective surfaces in an external electric field is discovered theoretically. The key mechanism of the instability is caused by Joule heating but dramatically differs from the well-known Raleigh-Benard convection. The investigation is based on the Nernst-Planck-Poisson-Navier-Stokes system along with the energy equation and corresponding BCs. The 1D quiescent steady state in microscales can be unstable with respect to either short-wave Rubinstein-Zaltzman or long-wave thermoelectokinenetic instability. The last one prevails in long microchannels and good enough thermal insulation of the system. In addition to the linear stability analysis a direct numerical simulation of the full 3D nonlinear system is fulfilled using a parallel computing. In the final coherent structures salt concentration, temperature and electric current are localized in narrow long fingers normal to the ion-selective surface while space charge forms crown-like micro-patterns. The investigation results can be useful in desalination problem. [Preview Abstract] |
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KP1.00053: Time-scale estimation of unstirred layer formation in osmotically driven flow. Tomoaki Itano, Taishi Inagaki, Keito Konno, Masako Sugihara-Seki We study the osmotic solvent flow driven by solute concentration difference across a semi-permeable membrane. The concentration difference across the membrane drives the solvent flow penetrating from the low concentration side through pores of the membrane. This spontaneous solvent flow transports solutes away from the membrane in the opposite side, which locally reduces the solute concentration in the vicinity of the membrane. The concentration boundary layer developed locally near the membrane in the case of absence of external stirring process was termed as “unstirred layer” in the previous studies, which has been recognized as a key of the unfavorable virtual resistance and membrane fouling in the water filtration of the desalination process. In the previous studies, the formation of the unstirred layer was analyzed under the assumption that the thickness of the unstirred layer is steady, which however contradicts the smoothness of the solute concentration at the end of the layer. In the present study, in order to resolve the contradiction, we assume the unsteadiness in the layer development so that the thickness of the unstirred layer may be estimated analytically. [Preview Abstract] |
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KP1.00054: Deposition of a large area of nanoparticles at an interface onto a substrate Duck-Gyu Lee, Thanh-Binh Nguyen, Hyuneui Lim Inspired by the antireflective function of moth eyes, attributing to the nanostructures on the surface of eyes, it has been a growing interest to fabricate a well-ordered array of nanoparticles. In this study, we demonstrated a simple fabrication method to generate a large area of close-packed nano-particles at a liquid-gas interface for depositing the particles onto a substrate. We experimentally found the optimal concentration of particles with a surfactant which enables the particles float at an interface in the form of a uniform array of particles. Then we gradually attached the array of particles to the surface of inclined substrate with an angle in water by reducing the level of water. It was observed that the flow rate of reducing water level and the inclination angle of the submerged substrate play an important role in determining the uniformity of the deposited monolayer on the substrates. To find the conditions under which the flow rate and the inclination make the uniform monolayer on the substrates, we made a regime map based on dimensionless parameters. [Preview Abstract] |
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KP1.00055: A DC electrophoresis method for determining electrophoretic mobility through the pressure driven negation of electro osmosis Pascal Karam, Sumita Pennathur Characterization of the electrophoretic mobility and zeta potential of micro and nanoparticles is important for assessing properties such as stability, charge and size. In electrophoretic techniques for such characterization, the bulk fluid motion due to the interaction between the fluid and the charged surface must be accounted for. Unlike current industrial systems which rely on DLS and oscillating potentials to mitigate electroosmotic flow (EOF), we propose a simple alternative electrophoretic method for optically determining electrophoretic mobility using a DC electric fields. Specifically, we create a system where an adverse pressure gradient counters EOF, and design the geometry of the channel so that the flow profile of the pressure driven flow matches that of the EOF in large regions of the channel (ie. where we observe particle flow). Our specific COMSOL-optimized geometry is two large cross sectional areas adjacent to a central, high aspect ratio channel. We show that this effectively removes EOF from a large region of the channel and allows for the accurate optical characterization of electrophoretic particle mobility, no matter the wall charge or particle size. [Preview Abstract] |
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KP1.00056: Optimal Spatial Scale for Curvature Calculations in Multiphase Flows Jacob Senecal, Mark Owkes In gas-liquid flows, the surface tension force often controls the dynamics of the flow and an accurate calculation of this force is necessary for predictive simulations. The surface tension force is directly proportional to the curvature of the gas-liquid interface, making accurate curvature calculations an essential consideration. Multiple methods have been developed to calculate the curvature of volume of fluid (VoF) interface capturing schemes, such as the height function method. These methods have been extensively tested. However, the impact of the scale or size of computational stencil on which the curvature is computed, has not been correlated with the rate at which interface perturbations relax under the surface tension force. In this work, the effect of varying the scale on which the curvature is computed has been tested and quantified. An optimal curvature scale is identified that leads to accurate and converging curvatures, and accurate timescales for surface tension induced, interface dynamics. [Preview Abstract] |
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KP1.00057: the God Particle {\&} the Delusion of Grandeur WH- Maksoed It had been established that it was crystalline The inner core is isolated from the rest of earth by the low-viscosity fluid outer core, and it can rotate, nod, precess, wobble, oscillate and even flip over, being only loosely constrained by the surrounding shells- Anderson, 2002. Furthers in accordances of PMRI from Dr.Robert K. Sembiring to ASTRANOMICS, herewith Richard Dawkins: \textbf{``the God delusion'' }-- 2006 ever quotes by the Rector of theUniversity of INDONESIA 2006 HE. Mr. Prof. Dr.derSoz Gumilar Rusliwa SOMANTRI: \textbf{``Beyond `delusion of grandeur' menuju INDONESIA baru Bebas Kemiskinan'' }ever retrieves Lester G. Telser- 1994: \textbf{``the Usefulness of Core Theory in Economics''} - ``core theory furnishes a useful framework for a wide variety of economic problems. It has an undeserved reputation of being too abstract owing mainly to the manner in which it is employed in the theory of general equilibrium.'' [Preview Abstract] |
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KP1.00058: Nanochannel arrays etched into hexagonal boron nitride mesa-membranes by focused ion beam. Remy Fulcrand, S\'ebastien Linas, Fran\c{c}ois Cauwet, Blaise Poinsot, Arnaud Brioude Meso-membranes with highly ordered nano channel arrays have been fabricated by patterning hexagonal boron nitride (h-BN) films using a focused ion beam. The complete experimental procedure will be given in detail form the chemical vapor deposition for h-BN synthesis to its patterning and the final membrane design for nanofluidic experiments. The membranes obtained are characterized at each experimental step by electron microscopy and Raman spectroscopy. The technique is finally applied to fabricate devices in which the only passage for a fluid is a nano channel array etched into a h-BN film. [Preview Abstract] |
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KP1.00059: The hydrodynamic interaction of two small freely-moving particles in a Couette flow of a yield stress fluid Mohammadhossein Firouznia, Bloen Metzger, Guillaume Ovarlez, Sarah Hormozi The flows of non-Newtonian slurries, often suspensions of noncolloidal particles in yield stress fluids, are ubiquitous in many natural phenomena and industrial processes. Investigating the microstructure is essential allowing the refinement of macroscopic equations for complex suspensions. One important constraint on the dynamics of a Stokesian suspension is reversibility, which is not necessarily valid for complex fluids. The interaction of two particles in a reversing shear flow of complex fluids is a guide to understand the behavior of complex suspensions. We study the hydrodynamic interaction of two small freely-moving spheres in a linear flow field of yield stress fluids. An important point is that non-Newtonian fluid effects can be varied and unusual. Depending on the shear rate, even a yield stress fluid might show hysteresis, shear banding and elasticity at the local scales that need to be taken into account. We study these effects with the aid of conventional rheometry, Particle Image Velocimetry and Particle Tracking Velocimetry in an original apparatus. We show our preliminary experimental results. [Preview Abstract] |
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KP1.00060: Strangely stable sphere stacking in yield-stress fluids Piyush Singh, Scott Rogman, Jonathan Freund, Randy Ewoldt We have previously observed a novel phenomenon whereby spheres sediment and form a single, stable vertical stack in a yield-stress fluid. Individually, the spheres settle to the bottom, since the yield stress is insufficient to suspend a single sphere. However, cooperative effects result in surprisingly stable stacking. Here, we further explore this phenomenon experimentally in a simple yield stress fluid, a carbopol microgel. Depending on the yield stress of the fluid, the sphere density, and the precise alignment of the spheres, a varying number of spheres can be stacked. Although a taller stack is observed for spheres of the same size, smaller stacks are frequently formed for spheres with mixed sizes and offset centers. This stacking phenomenon is not amenable to a simple force balance analysis because of the complex interplay of viscous and yield stresses and the non-trivial deformation zone in a yield-stress fluid. This study provides new insights on the collective flow behavior of objects in structurally complex and widely used yield-stress fluids. Furthermore, this observed phenomenon can be used to check the predictive efficacy of past, present, and future constitutive models for rheologically-complex fluids. [Preview Abstract] |
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KP1.00061: Dispersed phase effects on boundary layer turbulence David Richter, Brian Helgans In natural and environmental settings, turbulence is often seeded with some sort of dispersed phase: dust, rain, snow, sediment, etc. Depending on the circumstances, elements of the dispersed phase can participate in both dynamic and thermodynamic coupling, thereby altering the turbulent transfer of heat, moisture, and momentum through several complex avenues. In this study, evaporating droplets are two-way coupled to turbulent wall-bounded flow via direct numerical simulation (DNS) and Lagrangian point particle tracking, and we are specifically interested in the wall-normal transport of momentum, heat, and moisture. Our studies show that particles can carry significant portions of all three, and that this is a strong function of the particle Stokes number. These findings are interpreted in the context of environmental flows and the practical implications will be discussed. [Preview Abstract] |
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KP1.00062: Gravitational collapse of colloidal gels: Origins of the tipping point Poornima Padmanabhan, Roseanna Zia Reversible colloidal gels are soft viscoelastic solids in which durable but reversible bonds permit on-demand transition from solidlike to liquidlike behavior; these O(kT) bonds also lead to ongoing coarsening and age stiffening, making their rheology inherently time dependent. To wit, such gels may remain stable for an extended time, but then suddenly collapse, sedimenting to the bottom of the container (or creaming to the top) and eliminating any intended functionality of the material. Although this phenomenon has been studied extensively in the experimental literature, the microscopic mechanism underlying the collapse is not well understood. Effects of gel age, interparticle attraction strength, and wall effects all have been shown to affect collapse behavior, but the microstructural transformations underlying the ‘tipping point’ remain murky. To study this behavior, we conduct large-scale dynamic simulation to model the structural and rheological evolution of colloidal gels subjected to various gravitational stresses, examining the detailed micromechanics in three temporal regimes: slow sedimentation prior to collapse; the tipping point leading to the onset of rapid collapse; and the subsequent compaction of the material as it approaches its final bed height. [Preview Abstract] |
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KP1.00063: A study of thin-walled Taylor column under the influence of rotation Kuan-Ruei Lai, Chin-Chou Chu, Chien-Cheng Chang An extended study of thin-walled Taylor column under the influence of rotating cylinder is presented with very consistent results in numerical simulations and laboratory experiments. In the previous set-up, the Taylor column effect is produced under the influence of protruded cylinder from the top lid, and the thin-walled Taylor column is formed by draining of the fluid at the bottom. The primary interest of this study is to investigate the influence to thin-walled Taylor column when the cylinder is exerted with a relative rotation rate under very small Rossby number (\textit{Ro}$=U/$\textit{fR}) and Ekman number (\textit{Ek}$=\nu /$\textit{fR}$^{2})$. The flow patterns are performed with different cylinder height ratios ($h$/$H)$ along with varying relative rotation ratio of cylinder to the background $\alpha =\omega /\Omega $. Steady-state solutions being solved numerically in the rotating frame are shown to have good agreements with experimental flow visualizations on the resulting appearance of deformed thin-walled Taylor columns. As a result, the thin-walled Taylor column is observed to strengthen up with increasing $\alpha $, and weakens with decreasing $\alpha $. In addition, the weakening thin-walled Taylor column is observed to experience a break through transition near the bottom, which penetration diverged the recirculating region into two portions. [Preview Abstract] |
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KP1.00064: Effects pf Rounding on Flow Characteristics Past an Angulated Cylindrical Object Doohyun Park, Kyung-Soo Yang, Jaehee Kim In the present numerical study, we aim at elucidating the effects of rounding on flow topology past an angulated cylindrical object. Change in flow topology significantly affects flow-induced forces on the object. We consider the rounded cylinders ranging from a square cylinder of height $D$ to a circular cylinder of diameter $D$ by rounding the four corners of a square cylinder with a quarter circle of fixed radius ($r)$. An immersed boundary method was adopted for implementation of the cylinder cross-sections in a Cartesian grid system. The key parameters are Reynolds number (Re) and corner radius of curvature ($r)$. A small rounding delays the flow separation towards the trailing rounded edges, resulting in lower lift fluctuation. The minimum mean drag also occurs when the sharp edges of a square cylinder are “partially” rounded. The optimal edge-radius ratio ($r/d)$ for lift fluctuation or for mean drag depends upon \textit{Re}, and high-\textit{Re} flow tends to be more sensitive to small rounding. The main topological changes resulting from four-edge rounding can be obtained by leading-edge rounding alone. Trailing-edge rounding, however, plays a positive role in stabilizing the flow when the two types of rounding are combined. [Preview Abstract] |
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KP1.00065: Blast wave mitigation by dry aqueous foam: numerical modelling and experimental investigation. Denis Counilh, Felix Ballanger, Nicolas Rambert, Jean-Francois Haas, Aschwin Chinnayya, Alexandre Lefrancois Dry aqueous foams (two-phase media with water liquid fraction lower than 5{\%}) are known to mitigate blast wave effects induced by an explosion. The CEA has calibrated his numerical multiphase code MOUSSACA from shock tube and high-explosive experiments. The shock tube experiments have highlighted the foam fragmentation into droplets and the momentum transfer between the liquid and gas phases of the foam. More recently, experiments with hemispheric explosive charges from 3 g to 120 g have provided more findings about the pressure and impulse mitigation properties of foams. We have also taken into account the heat and mass transfer, as well as the droplets secondary breakup, characterized by the Weber number, ratio of inertia over surface tension. Good agreement is found between the calculation and the experiments. [Preview Abstract] |
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KP1.00066: 3D Lattice Boltzmann Modeling of Nanoparticle Self-Assembly in Evaporating Droplets and Rivulets Mingfei Zhao, Xin Yong In this work, a three-dimensional free-energy-based multiphase lattice Boltzmann method-Lagrangian particle tracking hybrid model is presented to simulate nanoparticle-laden droplets and rivulets undergoing evaporation. The 3D model enables the development of the 3D flow structures in the evaporating droplets, as well as allows us to capture the axial flows in the evaporating rivulets. We first model non-evaporating droplets and rivulets loaded with nanoparticles and the effects of particle-fluid interaction parameters on particle dynamics are characterized. By implementing evaporation, we probe the self-assembly of nanoparticles inside the fluid mass or at the liquid-vapor interface. The 3D microstructure of nanoparticle assemblies is quantified through radial distribution functions and structure factors. In particular, the final deposit of evaporating rivulets with oscillatory axial flows is revealed, resembling the flow field in printed rivulets in experiments. Our findings offer a theoretical framework to explore the dynamics of nanoparticle self-assembly in evaporating fluid mass. [Preview Abstract] |
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KP1.00067: Measuring Surface Tension of a Flowing Soap Film Aakash Sane, Ildoo Kim, Shreyas Mandre It is well known that surface tension is sensitive to the presence of surfactants and many conventional methods exist to measure it. These techniques measure surface tension either by intruding into the system or by changing its geometry. Use of conventional methods in the case of a flowing soap film is not feasible because intruding the soap film changes surface tension due to Marangoni effect. We present a technique in which we measure the surface tension in situ of a flowing soap film without intruding into the film. A flowing soap film is created by letting soap solution drip between two wires. The interaction of the soap film with the wires causes the wires to deflect which can be measured. Surface tension is calculated using a relation between curvature of the wires and the surface tension. Our measurements indicate that the surface tension of the flowing soap film for our setup is around 0.05 N/m. The nature of this technique makes it favorable for measuring surface tension of flowing soap films whose properties change on intrusion. [Preview Abstract] |
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KP1.00068: Geometric design of the best performing auto-rotating wing Yucen Liu, Lionel Vincent, Eva Kanso Many plants use gravity and aerodynamics to disperse their seeds away from the parent plant. Various seed designs result in different dispersal modes from gliding to auto-rotating. Here, we are interested in understanding the effect of geometric design of auto-rotating seedpods on their aerodynamic performance. As an experimentally tractable surrogate to real seedpods, we investigate auto-rotating paper wings of various shape designs. We compare these designs to a control case consisting of the canonical rectangular wing. Inspired by aerodynamics, we begin by considering the benefit of an elliptical planform, and test the effect of aspect ratio on flight range and descent angle. We find the elliptical planform improves the tumbling rate and the aspect ratio has a positive effect on the flight performance of the wings. We then test two families of more complex shapes: one of tapered planform and one of a planform with sharp tips. We look for an optimal flight performance while constraining either the mass or the maximum length and width of the wing. We find that wings with sharper tips and larger length have higher auto-rotation rates and improved performance. The results imply that both the planform and length of the wing contribute to the wing’s flight performance. [Preview Abstract] |
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KP1.00069: Dynamics of a high viscosity layer in response to shear flow Ehsan Esmaili, Anne Staples We use the Shan-Chen multicomponent Lattice Boltzmann method (LBM) to investigate the time evolution of a thin liquid film (phase I) coating a solid surface under the action of a shearing force imposed by a surrounding fluid (phase II), whose viscosity is significantly lower than that of the film. The goal of this study is to use LBM to capture the contact line motion and interfacial dynamics for an oil-like liquid film which is driven by the upper phase (water) movement as a first approach to modeling thin film dewetting in wave swept marine environments. Lubrication theory is used to validate the results for the driven thin film, and the LBM simulations investigate the effects of the upper phase movement, lower phase thickness, and angle of the imposed shearing force on the thin film profile. [Preview Abstract] |
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KP1.00070: Droplet Impact on a Heated Surface under a Depressurized Environment Ryuta Hatakenaka, Yoshiyuki Tagawa Behavior of a water droplet of the diameter 1-3mm impacting on a heated surface under depressurized environment (100kPa -1kPa) has been studied. A syringe pump for droplet generation and a heated plate are set into a transparent acrylic vacuum chamber. The internal pressure of the chamber is automatically controlled at a target pressure with a rotary pump, a pressure transducer, and an electrical valve. A silicon wafer of the thickness 0.28 mm is mounted on the heater plate, whose temperature is directly measured by attaching a thermocouple on the backside. The droplet behavior is captured using a high-speed camera in a direction perpendicular to droplet velocity. Some unique behaviors of droplet are observed by decreasing the environmental pressure, which are considered to be due to two basic elements: Enhancement of evaporation due to the lowered saturation temperature, and shortage of pneumatic spring effect between the droplet and heated wall due to the lowered pressure of the air. [Preview Abstract] |
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KP1.00071: Modeling flow for modified concentric cylinder rheometer geometry Karen Ekeruche, Kelly Connelly, H. Pirouz Kavehpour Rheology experiments on biological fluids can be difficult when samples are limited in volume, sensitive to degradation, and delicate to extract from tissues. A probe-like geometry has been developed to perform shear creep experiments on biological fluids and to use the creep response to characterize fluid material properties. This probe geometry is a modified concentric cylinder setup, where the gap is large and we assume the inner cylinder rotates in an infinite fluid. To validate this assumption we perform shear creep tests with the designed probe on Newtonian and non-Newtonian fluids and vary the outer cylinder container diameter. We have also created a numerical model based on the probe geometry setup to compare with experimental results at different outer cylinder diameters. A creep test is modeled by applying rotation to the inner cylinder and solving for the deformation of the fluid throughout the gap. Steady state viscosity values are calculated from creep compliance curves and compared between experimental and numerical results. [Preview Abstract] |
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KP1.00072: Symbolic dynamics applied to a numerical simulation of a perturbed Hill's spherical vortex. Joshua Arenson, Spencer Smith, Kevin Mitchell In the classic Hill's spherical vortex flow an invariant sphere prevents material inside the vortex from mixing with material outside. Here, we apply an additional shear and rotational flow to break the symmetry of the vortex, thereby allowing mixing of the material inside and outside. The resulting system exhibits fully 3D chaotic advection. We consider the scattering of passive tracers that are drawn into and then ejected from the vortex. Here we focus on the numerical computation of fractal scattering functions--the time trapped within the vortex as a function of two impact parameters. We then compare the fractal self-similarity of these scattering functions to those predicted by 3D homotopic lobe dynamics--a new symbolic method of describing topological dynamics. [Preview Abstract] |
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KP1.00073: Onset of flow instability in rigid foams Carlos Andrés Barros Ochoa, Petr Denissenko, Carlos Alberto Duque Daza The flow transition between stationary and time dependent regimes at the exit of a block of open-cell foam has been examined experimentally using Laser Doppler Anemometry. Measurements have been conducted at three points located at a plane located 10 mm downstream from the exit of the foam. The streamwise component of fluid velocity was measured at multiple flow rates. The probability density function of the velocity is two-peaked at Reynolds numbers above 25 based on the average pore size and is a skewed one-peak distribution at lower flow rates. Numerical simulations are being conducted using a computer tomography scanned model of the foam to match the experimental measurements. Obtained results are discussed in the context of using the open-cell foams in catalytic reactors. [Preview Abstract] |
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KP1.00074: Prediction of Algebraic Instabilities Paula Zaretzky, Kristina King, Nicole Hill, Kimberlee Keithley, Nathaniel Barlow, Steven Weinstein, Michael Cromer A widely unexplored type of hydrodynamic instability is examined - large-time algebraic growth. Such growth occurs on the threshold of (exponentially) neutral stability. A new methodology is provided for predicting the algebraic growth rate of an initial disturbance, when applied to the governing differential equation (or dispersion relation) describing wave propagation in dispersive media. Several types of algebraic instabilities are explored in the context of both linear and nonlinear waves. [Preview Abstract] |
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KP1.00075: STUDENT POSTER COMPETITION: COMPUTATIONS |
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KP1.00076: Harnessing Energy from Arrays of Oscillating Hydrofoils Filip Simeski, Arianne Spaulding, Jennifer Franck Computational Fluid Dynamics (CFD) simulations are performed on multiple-hydrofoil systems for the application of energy harvesting. Oscillating hydrofoils generate power through a coupled heaving and pitching motion. Various linear and staggered configurations consisting of three to four hydrofoils are simulated, and the system efficiency of the array is evaluated, as well as the energy density of the system. Of particular interest is the observation that regular vortices from the foils’ leading and trailing edges develop into a well-structured wake affecting performance of downstream-located hydrofoils in the system, and leading to an optimal phase difference between foils. Simulations are performed at a Reynolds number of 1000, and utilize OpenFOAM with dynamic meshing libraries employed to handle the foil motion. [Preview Abstract] |
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KP1.00077: Numerical analysis of the inertial migration of a spherical particle in circular tube flows Takuya Yabu, Tomoaki Itano, Masako Sugihara-Seki In a study of dilute suspension flow through circular tubes, Segr\'{e} \& Silberberg (1961) reported lateral migration of neutrally buoyant spherical particles to an equilibrium radial position at low Reynolds numbers (Re). A later experimental study by Matas et al. (2004) found that another equilibrium annulus (inner annulus) emerges closer to the tube center at elevated Re. Since existing theoretical studies based on the matched asymptotic expansion could not account for the appearance of the inner annulus, the present study aimed to investigate numerically the equilibrium positions of a rigid spherical particle suspended in a Poiseuille flow for 100 $<$ Re $<$1,500. In the case of particle to tube diameter ratios \~ 0.1, the flow field around the particle was computed by the immersed boundary method to calculate the lateral force exerted on the particle. It was found that for Re $<$ 1,000, the lateral force vanishes at a single radial position, corresponding to the so-called Segr\'{e}-Silberberg annulus, whereas beyond this Re, a new equilibrium position appears closer to the tube center, possibly representing the inner annulus. In addition, it was predicted that for Re $>$ 1,200, the Segr\'{e}-Silberberg annulus disappears and only the inner annulus retains. [Preview Abstract] |
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KP1.00078: On the Structure Orientation in Rotating and Sheared Homogeneous Turbulence Joylene C. Aguirre, Adam F. Moreau, Frank G. Jacobitz The results of direct numerical simulations are used to study the effect of rotation on the orientation of structures and the evolution of the turbulent kinetic energy in homogeneous sheared turbulence. Shear flows without rotation, with moderate rotation, and with strong rotation are considered and the rotation axis is either parallel or anti-parallel to the mean flow vorticity. In the case of moderate rotation, an anti-parallel configuration increases the growth rate of the turbulent kinetic energy, while a parallel configuration decreases the growth rate as compared to the flow without rotation. The orientation of turbulent structures present in the flows are characterized using the three-dimensional, two-point autocorrelation coefficient of velocity magnitude and vorticity magnitude. An ellipsoid is fitted to the surface defined by a constant autocorrelation coefficient value and the major and minor axes are used to determine the inclination angle of flow structures in the plane of shear. It was found that the inclination angle assumes a maximum value for the anti-parallel configuration with moderate rotation. Again, the inclination angle for the parallel configuration with moderate rotation is reduced as compared to the case without rotation. The smallest inclination angles are found for the strongly rotating cases. Hence, the inclination angle is directly related to the growth rate of the turbulent kinetic energy. [Preview Abstract] |
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KP1.00079: Aerodynamic Analysis of Morphing Blades Caleb Harris, David MacPhee, Madeline Carlisle Interest in morphing blades has grown with applications for wind turbines and other aerodynamic blades. This passive control method has advantages over active control methods such as lower manufacturing and upkeep costs. This study has investigated the lift and drag forces on individual blades with experimental and computational analysis. The goal has been to show that these blades delay stall and provide larger lift-to-drag ratios at various angles of attack. Rigid and flexible airfoils were cast from polyurethane and silicone respectively, then lift and drag forces were collected from a load cell during 2-D testing in a wind tunnel. Experimental data was used to validate computational models in OpenFOAM. A finite volume fluid-structure-interaction solver was used to model the flexible blade in fluid flow. Preliminary results indicate delay in stall and larger lift-to-drag ratios by maintaining more optimal angles of attack when flexing. [Preview Abstract] |
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KP1.00080: Numerical simulation of microlayer formation in nucleate boiling Alexandre Guion, Jacopo Buongiorno, Shahriar Afkhami, Stephane Zaleski Numerical simulations of boiling resolve the macroscopic liquid-vapor interface of the bubble, but resort to subgrid models to account for microscale effects, such as the evaporation of the liquid microlayer underneath the bubble. Realistic time-dependent microlayer evaporation models necessitate initialization of the microlayer profile. In the recent simulations published in the literature [J. Comp. Phys., 300 (2015): 20-52], missing input data on initial microlayer geometry is replaced by estimated values from separate experimental measurements at similar pressure. Yet, the geometry of the initial microlayer not only depends on pressure for a given set of fluids, but also on bubble growth rate and that dependence is not known {\it a priori}. In this work, the Volume-of-Fluid (VOF) method, implemented in the open-source code Gerris (gfs.sf.net), is used to simulate, with unprecedented accuracy, the dynamics of microlayer formation underneath a growing bubble. A large numerical database is generated, yielding the microlayer thickness during the inertia controlled phase of bubble growth as a function of radial distance from the bubble root, time, contact angle, and capillary number associated with bubble growth. No significant dependence on density or viscosity ratios were found. [Preview Abstract] |
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KP1.00081: A nonlinear dynamical system for combustion instability in a pulse model combustor Kazushi Takagi, Hiroshi Gotoda We theoretically and numerically study the bifurcation phenomena of nonlinear dynamical system describing combustion instability in a pulse model combustor on the basis of dynamical system theory and complex network theory. The dynamical behavior of pressure fluctuations undergoes a significant transition from steady-state to deterministic chaos via the period-doubling cascade process known as Feigenbaum scenario with decreasing the characteristic flow time. Recurrence plots and recurrence networks analysis we adopted in this study can quantify the significant changes in dynamic behavior of combustion instability that cannot be captured in the bifurcation diagram. [Preview Abstract] |
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KP1.00082: Is the stokeslet model sufficient for finding nutrient uptake of microscopic suspension feeders? Alexander T. Lutton, Rachel E. Pepper Microscopic sessile suspension feeders are part of many aquatic ecosystems. They are single-celled, vary in size from a few to about 100 microns in length, live attached to substrates, and serve important ecological roles as both food for larger organisms and consumers of bacteria and other small particles. These organisms create currents in order to bring food toward them. Understanding these currents may allow us not only deeper insight into the ecology of aquatic ecosystems, but also may enable innovation in water treatment. Simulations of the feeding currents of these organisms typically use a simple model that places a stokeslet above an infinite plane boundary representing the surface of attachment. This model produces a useful approximation for the flow field of the organism, but may be of limited accuracy when the organism is near the boundary. We create a different model composed of a stokeslet and a potential dipole, which form a sphere. This sphere has a sin($\theta )$ tangential velocity boundary condition, accounting for the cell body. Using nutrient flux to the organism as our metric, we investigate the discrepancy between the spherical and stokeslet models in order to determine the efficacy of the stokeslet model as an approximation of single-celled suspension feeders. [Preview Abstract] |
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KP1.00083: STUDENT POSTER COMPETITION: EXPERIMENTS |
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KP1.00084: An experimental study of low Re cavity vortex formation embedded in a laminar boundary layer Sashank Gautam, Amy Lang, Jacob Wilroy Laminar boundary layer flow across a grooved surface leads to the formation of vortices inside rectangular cavities. The nature and stability of the vortex inside any single cavity is determined by the Re and cavity geometry. According to the hypothesis, under low Re and stable vortex conditions a single cavity vortex leads to a roller-bearing effect which results in a decrease in drag as quantified by velocity profiles measured within the boundary layer. At higher Re once the vortex becomes unstable, drag should increase due to the mixing of low-momentum fluid within the cavity and the outer boundary layer flow. The primary objective of this experiment is to document the phenomenon using DPIV in a tow tank facility. This study focuses on the transition of the cavity flow from a steady to an unsteady state as the Re is increased above a critical value. The change in boundary layer momentum and cavity vortex characteristics are documented as a function of Re and boundary layer thickness. [Preview Abstract] |
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KP1.00085: An experimental investigation of blast driven turbulence Benjamin Musci, Devesh Ranjan In the Georgia Tech Shock and Advanced Mixing Lab, a facility is being built to study blast driven turbulence. Motivated by the discrepancies observed between actual and modeled supernovae, this facility aims to resolve the important spatial scales in the extensive mixing of the outer layers. These outer layers will be modeled by subjecting two-three gases of varying density to a blast wave generated by Exploding Bridge Wires. The blast wave's interaction with perturbations at the gaseous, membrane-less, interfaces will induce the Richtmeyer-Meshkov or Rayleigh Taylor Instability, depending on the acceleration history and perturbation amplitude. Through the use of simultaneous Particle Image Velocimetry, and Planar Laser Induced Fluorescence, this project aims to determine the effect of interface initial conditions on turbulence. A 2D Diverging Wedge and 3D Diverging Conical Tube are being built to enable repeatable blast-wave production, continuous optical viewing of the flow, reproducible multi-layer interface creation, and the collection of simultaneous density-velocity measurements to directly measure turbulent quantities. The preliminary analysis informing the design of this facility, the construction progress, and updates on newly realized design constraints are presented. [Preview Abstract] |
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KP1.00086: Flexible Blades for Wind Turbines Madeline Carlisle Collins, David MacPhee, Caleb Harris Previous research has shown that windmills with flexible blades are more efficient than those with rigid blades. Flexibility offers passive pitch control, preferable to active pitch control which is costly and requires maintenance. Flexible blades morph such that the blade more closely resembles its design point at part load and over load. The lift-to-drag ratios on individual blades was investigated. A mold was designed and machined from an acrylic slab for the casting of blades with a NACA 0012 cross section. A flexible blade was cast from silicone and a rigid blade was cast from polyurethane. Each of these blades was tested in a wind tunnel, cantilever mounted, spanning the whole test section. The angle of attack was varied by rotating the mount. All tests were performed at the same wind speed. A load cell within the mount measured forces on the blade, from which the lift and drag forces were calculated. The stall point for the flexible blade occurred later than for the rigid blade, which agrees with previous research. Lift-to-drag ratios were larger for the flexible blade at all angles of attack tested. Flexible blades seem to be a viable option for passive pitch control. Future research will include different airfoil cross sections, wind speeds, and blade materials. [Preview Abstract] |
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KP1.00087: CLOUD-MAP Field Campaign Measurements of the Earth's Lower Boundary Layer Nicholas Foster, Alyssa Avery, Jamey Jacob CLOUD-MAP (Collaboration Leading Operational UAS Development for Meteorology and Atmospheric Physics) is a 4 year, 4 university collaboration to develop capabilities that will allow meteorologists and atmospheric scientists to use unmanned aircraft as a common, useful everyday tool. Currently, we know that systems can be used for meteorological measurements, but they are far from being practical or robust for everyday field diagnostics by the average meteorologist or scientist. In particular, UAS are well suited for the lower atmosphere, namely the lower boundary layer that has a large impact on the atmosphere and where much of the weather phenomena begin. A sensor set called MDASS (Meteorological Data Acquisition Sonde System) was developed and used to collect and transmit live data necessary for developing such forecasts as well as be usable on multiple platforms ranging from fixed-wing and multi-rotor UAVs to rockets. The data transmitted from MDASS is viewed and stored on a ground control station via LabVIEW in a program developed for real-time data analysis. Results from the first CLOUD-MAP are presented. The campaign resulted in nearly 250 unmanned aircraft flights of 12 separate platforms over a 3 day period, collecting meteorological data at 3 different sites. [Preview Abstract] |
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KP1.00088: STUDENT POSTER COMPETITION: MICROFLUIDICS AND INTERFACES |
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KP1.00089: High-speed ethanol micro-droplet impact on a solid surface Yuta Fujita, Akihito Kiyama, Yoshiyuki Tagawa Recently, droplet impact draws great attention in the fluid mechanics. In previous work, micro-droplet impact on a solid surface at velocities up to 100 m s$^{\mathrm{-1}}$ was studied. However the study was only on water micro-droplets. In this study, we experimentally investigate high-speed impact of ethanol micro-droplets in order to confirm the feature about maximum spreading radius with another liquid. A droplet is generated from a laser-induced high-speed liquid jet. The diameter of droplets is around 80 $\mu $m and the velocity is larger than 30 m s$^{\mathrm{-1}}$. The surface tension of ethanol is 22.4 mNm$^{\mathrm{-1}}$ and density is 789 kgm$^{\mathrm{-3}}$. Weber number ranges We \textgreater 1000. By using a high-speed camera, we investigate the deformation of droplets as a function of Weber number. [Preview Abstract] |
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KP1.00090: The injection of a highly focused microjet into a soft target Nanami Endo, Sennosuke Kawamoto, Yoshiyuki Tagawa Needle-free drug injection systems have been developed in order to supersede traditional syringe injection system with needles. However, in spite of its great potential, these systems are not commonly used. One of the main reasons is to use diffusive jets, which results in severe deceleration of the jets and causes insufficient penetration. Recently, a highly focused microjet generated by irradiating a laser pulse to a point inside a liquid filled in a capillary tube is gathering attention as a method to solve these problems. Although the microjet injection phenomena into a model material of the skin have been studied, the effect of the distance R (R is a distance between a gas-liquid interface and a target) on injection phenomena have not been researched. The distance R is not a parameter which controls the jet generation. However, considering the practical use of the needle-free injection, it is necessary to know appropriate value of the distance R. In this study, we change the distance R in a range of 0.3 mm to 5 mm to investigate its influence on the injection depth Di. As a target, we used 5 wt{\%} gelatin. We show relationship between injection depth Di and distance R and rationalize it in this presentation. [Preview Abstract] |
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KP1.00091: How does the micro-splashing threshold change with drop size? Sam J. Boos, Rachel E. Pepper Micro-splashing is a newly discovered type of splashing that appears within microseconds of first contact between liquid drop and surface, producing tiny droplets with diameters of approximately 10-50 $\mu $m. The droplets are ejected outwards at speeds over ten times that of the parent drop. Previously discovered splashing phenomena, like prompt or corona splashing, happen much later in the drop impact and produce larger, slower droplets compared to micro-splashing. A greater understanding of micro-splashing may be important in industry and global health because micro-splashes may, for example, affect the quality of ink printing or contribute to atmospheric aerosolization of particles and toxins. An initial study (Thoroddsen ST, Takehara K, Etoh TG. J. Fluid Mech. 706 (2012)) discovered this new type of splashing, described the nature of the micro-splashes, and proposed a mechanism behind their generation. However, micro-splashing is yet to be fully understood. We use high-speed video to determine how drop size affects the threshold velocity for micro-splashing, as a step towards further understanding this phenomenon. [Preview Abstract] |
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KP1.00092: Separating Particles Using Tangential Flow Filtration and Inertial Microfluidics Amanda Singleton, Mike Garcia, Sumita Pennathur The separation of micron-sized particles is a crucial component in a myriad of applications. Recently researchers have attempted to use inertial microfluidics to separate particles because the technique requires smaller sample volume, has a high throughput, and is inherently robust. ~Unfortunately, inertial microfluidics lacks versatility: geometric considerations limit variation of particle size. To overcome this limitation, we experimentally investigate the effect of adding permeate flow to refocus particles into tunable equilibrium locations. ~Specifically, we experimentally investigate the effect of permeate flow on the equilibrium location of 5, 10, and 15-micron polystyrene particles in a MEMS fabricated tangential flow filtration device. We see that contrary to inertial focusing in straight microfluidic channels, smaller particles focus closer to the center than larger particles. Furthermore, the particle equilibrium location is a function of streamwise distance, and equilibrium location at the exit is a function of the ratio of outlet to inlet flow. Taking advantage of this data, we aim to create in-situ control of particle equilibrium locations resulting in real time separations of particles of unknown size distribution. This method can be combined with on-chip devices for diagnostic applications, benefitting the fluids and separations community [Preview Abstract] |
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KP1.00093: Three-dimensional wave evolution on electrified falling films. Ruben Tomlin, Demetrios Papageorgiou, Greg Pavliotis We consider the full three-dimensional model for a thin viscous liquid film completely wetting a flat infinite solid substrate at some non-zero angle to the horizontal, with an electric field normal to the substrate far from the flow. Thin film flows have applications in cooling processes. Many studies have shown that the presence of interfacial waves increases heat transfer by orders of magnitude due to film thinning and convection effects. A long-wave asymptotics procedure yields a Kuramoto-Sivashinsky equation with a non-local term to model the weakly nonlinear evolution of the interface dynamics for overlying film arrangements, with a restriction on the electric field strength. The non-local term is always linearly destabilising and produces growth rates proportional to the cube of the magnitude of the wavenumber vector. A sufficiently strong electric field is able promote non-trivial dynamics for subcritical Reynolds number flows where the flat interface is stable in the absence of an electric field. We present numerical simulations where we observe rich dynamical behavior with competing attractors, including ``snaking'' travelling waves and other fully three-dimensional wave formations. [Preview Abstract] |
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KP1.00094: Towards designing miniature surfing robots Saeed Jafari Kang, Vahid Vandadi, Hassan Masoud We theoretically study the surfing motion of chemically and thermally active particles located at a flat liquid-gas interface that sits above a liquid layer of finite depth. The particles' activity creates and maintains a surface tension gradient resulting in the auto-surfing. It is intuitively perceived that Marangoni surfers propel towards the direction with a higher surface tension. Remarkably, we find that the surfers may propel in the lower surface tension direction depending on their geometry and proximity to the bottom of the liquid layer. In particular, our analytical calculations for Stokes flow and diffusion-dominated scalar (i.e. chemical concentration and temperature) fields indicate that spherical particles undergo reverse Marangoni propulsion under confinement whereas disk-shaped surfers always move in the expected direction. We extend our results by proposing an approximate formula for the propulsion speed of oblate spheroidal particles based on the speeds of spheres and disks. Overall, our findings pave the way for designing microsurfers capable of operating in bounded environments. [Preview Abstract] |
(Author Not Attending)
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KP1.00095: The use of micro-/milli- fluidics to better understand the mechanisms behind deep venous thrombosis Zoe Schofield, Alessio Alexiadis, Alexander Brill, Gerard Nash, Daniele Vigolo Deep venous thrombosis (DVT) is a dangerous and painful condition in which blood clots form in deep veins (e.g., femoral vein). If these clots become unstable and detach from the thrombus they can be delivered to the lungs resulting in a life threatening complication called pulmonary embolism (PE). Mechanisms of clot development in veins remain unclear but researchers suspect that the specific flow patterns in veins, especially around the valve flaps, play a fundamental role.Here we show how it is now possible to mimic the current murine model by developing micro-/milli-fluidic experiments. We exploited a novel detection technique, ghost particle velocimetry (GPV), to analyse the velocity profiles for various geometries. These vary from regular microfluidics with a rectangular cross section with a range of geometries (mimicking the presence of side and back branches in veins, closed side branch and flexible valves) to a more accurate venous representation with a 3D cylindrical geometry obtained by 3D printing. In addition to the GPV experiments, we analysed the flow field developing in these geometries by using computational fluid dynamic simulations to develop a better understanding of the mechanisms behind DVT. [Preview Abstract] |
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KP1.00096: POSTDEADLINE |
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KP1.00097: Communication of Information with Sub-particles (Sub-strings) from Fifth Dimension of the Universe (Information) as the ``Fundamental Symmetry'' in the Nature Hassan Gholibeigian, Ghsem Gholibeigian, Abdolazim Amirshahkarami, Kazem Gholibeigian All fundamental particles (strings) getting information from their four animated sub-particles (sub-strings) after processing by them for motion [Gholibeigian, APS April Meeting 2015, abstract {\#}L1.027]. It seems that the source of information which particles and dark mater/energy are floating in it and whispering to its communication may be ``fifth dimension'' of the nature after space-time dimensions. In other words, the space-time can be the universe's hardware and information's dimension can be dynamic software of the universe which has always become up to date. Communication of information has a vital role in creation and evolution of the universe, may be as the ``fundamental symmetry'' in the nature, which began before the spark to B.B. (Convection Bang), and leads other symmetries and supersymmetry as well as other phenomena. Duration of the before Planck time, from $0\to 10^{-44}$ second, and its correspondence space which its result was generation of the very hot and energetic point for the B.B. / C.B. needed to communication of information. It seems that this fifth dimension has appeared for leading the processes before and after Planck time. How this dimension of the nature appeared and has always become up to date? [Preview Abstract] |
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KP1.00098: Embedding of electrodes within a microchannel interfacing a permselective medium for sensing and active control of the concentration-polarization layer Gilad Yossifon, Sinwook Park Previously, it has been shown that for a prescribed system, the diffusion length may be affected by any number of mechanisms including natural and forced convection, electroosmotic flow of the second kind and electro-convective instability. In all of the above mentioned cases the length of the diffusion layer is indirectly prescribed by the complicated competition between several mechanisms which are primarily dictated by the various system parameters and applied voltage. In contrast, we suggest that by embedding electrodes/heaters within a microchannel interfacing a permselective medium, the diffusion layer length may be controlled regardless of the dominating overlimiting current mechanism and system parameters. As well as demonstrating that the simple presence of electrodes can enhance mixing via induced-charge electrokinetic effects, we also offer a means of externally activating embedded electrodes and heaters to maintain external, dynamic control of the diffusion length. Such control is particularly important in applications requiring intense ion transport, such as electrodialysis. At the same time, we will also investigate means of suppressing these mechanisms which is of fundamental importance for sensing applications. [Preview Abstract] |
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KP1.00099: Experimental study of the submerged jet flow from a circular orifice for low values of Reynolds (Re) number. Ayax Hernando Torres Victoria, Mario Alberto Sánchez Rosas, Juan Casillas Navarrete, Fernando Aragón Rivera, José Alfredo Jiménez Bernal, Abraham Medina Ovando The results of the experimental study of the submerged jet flow emerging from a circular orifice, where the fluid injected and the fluid in the receiving volume are the same, are presented in this work. Velocity vector fields for Reynolds (Re) 2, 4, 6, 8, 10 {\&} 20 were obtained by means of the PIV technique. Similarly, results for the inward flow for the same geometry and Reynolds (Re) numbers are presented. Velocity profile plots and streamlines, for their corresponding Reynolds (Re) value, are also presented. [Preview Abstract] |
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KP1.00100: Theoretical study of instability observed inside a precessing cylinder Waleed Mouhali, Thierry Lehner, Aziz Salhi Cyclones have been observed in our experiment involving water in a both rotating and precessing cylinder. The following mechanism can explain their generation: first the mode coupling of two inertial waves with azimuthal wavenumber m$=$0 and m$=$1 (mode forced by the precession) in the inviscid regime (at high Re numbers) creates a differential rotation regime which has been observed in the same experiment~at small enough Poincar\'{e} number $\varepsilon $ (ratio of the precession to the rotation frequencies). Secondly, the radial profile of the corresponding axial mean flow vorticity shows an inflection point leading to a localized inflectional/shear secondary instability. We show that when the parameter $\varepsilon $ is increased from low values the mode m$=$0 becomes the most unstable one in this induced differential rotation at a reproducible threshold in $\varepsilon $, which can induce further the observed cyclones. In addition radial jets coming from the lateral boundary layers have been also observed which can drive additional cyclones by another instability developing in the boundary shear layer in presence of radial flow. [Preview Abstract] |
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KP1.00101: The effect of changing topography on coastal tides and storm surge: a historical perspective Stefan Talke, David Jay, Lumas Helaire, Ramin Familkhalili Over decadal and century time scales, the topography of coastal harbors changes due to natural and anthropogenic factors. These changes alter the mass and momentum balances of incoming waves, producing measureable changes to tides and surge. Here we use recently recovered archival data, historic bathymetric charts, and numerical models to assess changes in multiple estuaries. In the Columbia River estuary, Ems estuary, and Cape Fear Estuary , channel deepening has increased the M2 tide between 10 to 100{\%} since the 19$^{\mathrm{th}}$ century, due to both reduced frictional effects and altered resonance. The bathymetric perturbations also affect the propagation of other long-period waves: in Wilmington (NC), the worst-case scenario CAT-5 storm surge is modeled to increase by 50{\%} since 19$^{\mathrm{th}}$ century conditions. Similarly, in New York harbor, the 10 year storm-tide level has outpaced sea-level rise by nearly 30 cm since 1850. In the Columbia River, reduced friction has decreased the river slope (reducing water levels), but also led to amplification of both tides and flood waves. Going forward, historical bathymetric change may provide a clue to the future effects of climate change and continued anthropogenic development. [Preview Abstract] |
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KP1.00102: The control effect in a detached laminar boundary layer of an array of normal synthetic jets. Fernando Valenzuela Calva, Ruben Avila Rodriguez In this work, 3D numerical simulations of an array of three normal circular synthetic jets embedded in an attached laminar boundary layer that separates under the influence of an inclined flap are performed for flow separation control. At the beginning of the present study, three cases are used to validate the numerical simulation with data obtained from experiments. The experimental data is chosen based on the cases which presented higher repeatability and reliability. Simulations showed reasonable agreement when compared with experiments. The simulations are undertaken at three synthetic jet operating conditions, i.e. Case A: $L =$ 2, \textit{VR }$=$ 0.32; Case B: $L =$ 4, \textit{VR }$=$ 0.64 and Case C: $L =$ 6, \textit{VR }$=$ 0.96. The vortical structures produced for each synthetic jet operating condition are hairpin vortices for Case A and tilted vortices for Case B and C, respectively. By examining the spatial wall shear stress variations, the effect on the boundary layer prior to separation of the middle synthetic jet is evaluated. For effective flow control, produced at a relatively low \begin{figure}[htbp] \centerline{\includegraphics[width=0.22in,height=0.20in]{110820161.eps}} \label{fig1} \end{figure} the finding from this study suggests that hairpin vortical structures are more desirable structures. [Preview Abstract] |
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KP1.00103: Defects at the Nanoscale Impact Contact Line Motion at all Scales Hugo Perrin, Bruno Andreotti, Romain Lhermerout, Kristina Davitt, Etienne Rolley The contact angle of a liquid drop moving on a real solid surface depends on the speed and direction of motion of the three-phase contact line. Many experiments have demonstrated that pinning on surface defects, thermal activation and viscous dissipation impact contact line dynamics, but so far efforts have failed to disentangle the role of each of these dissipation channels. Here, we propose a unifying multi-scale approach that provides a single quantitative framework. We use this approach to successfully account for the dynamics measured in a classic dip-coating experiment performed over a unprecedentedly wide range of velocity. We show that the full contact line dynamics up to the liquid film entrainment threshold can be parametrized by the size, amplitude and density of nanometer-scale defects. This leads us to reinterpret the contact angle hysteresis as a dynamical cross-over rather than a depinning transition. [Preview Abstract] |
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KP1.00104: Numerical simulation of convective evaporation of a droplet on a porous surface Moonhyeok Choi, Gihun Son Numerical simulation is performed for droplet evaporation on a porous surface under an external flow condition. The droplet interface is tracked by a level-set (LS) method, which is modified to include the effects of porosity and evaporation coupled to heat and mass transfer. The conservation equations of mass, momentum, energy and vapor fraction for the external fluid region are combined with the local volume averaged conservation equations for the porous region through the matching conditions of velocity, pressure, temperature and vapor fraction at the fluid-solid interface. The temperature and the vapor fraction at the liquid-gas interface and the evaporation mass flux are simultaneously determined from the coupled equations for the mass and energy balances at the interface and the thermodynamic relation. The numerical simulation demonstrates the droplet penetration into the porous region and the evaporation to the porous and external flow regions. The effects of external flow velocity, porosity and porous particle size on the droplet deformation and evaporation are investigated. [Preview Abstract] |
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KP1.00105: Numerical analysis of bubble-cluster formation in an ultrasonic field Donghyun Kim, Gihun Son Bubble-cluster formation in an ultrasonic field is investigated numerically solving the conservation equations of mass, momentum and energy. The liquid-gas interface is calculated using the volume-of-fluid method with variable gas density to consider the bubble compressibility. The effect of liquid-gas phase change is also included as the interface source terms of the mass and energy equations. The numerical approach is tested through the simulation of the expansion and contraction motion of a compressed bubble adjacent to a wall. When the bubble is placed in an ultrasonic field, it oscillates radially and then collapses violently. Numerical simulation is also performed for bubble-cluster formation induced by an ultrasonic generator, where the generated bubbles are merged into a macrostructure along the acoustic flow field. The effects of ultrasonic power and frequency, liquid properties and pool temperature on the bubble-cluster formation are investigated. [Preview Abstract] |
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KP1.00106: Macromolecular Origins of Harmonics Higher than the Third in Large-Amplitude Oscillatory Shear Flow Alan Giacomin, Layal Jbara, Peter Gilbert In 1935, Andrew Gemant conceived of the complex viscosity, a~rheological material function measured~by "jiggling" an~elastic liquid in oscillatory shear [\textit{Rheol. Acta},~\textbf{51}, 481 (2012)].~~This test reveals information about both~the viscous and elastic properties of the liquid, and about~how these~properties depend on frequency. ~The test gained popularity with~chemists when John Ferry perfected instruments for measuring~both the real~and imaginary parts of the complex viscosity [\textit{Mem. Trib., NAE},~\textbf{17}, 96 (2013)]. ~In 1958,~Cox and Merz~discovered that the steady shear viscosity curve was easily~deduced from the magnitude of the complex viscosity, and today~ oscillatory shear is the single most popular rheological property measurement. With oscillatory shear, we can control two things: the frequency~(Deborah number) and the shear rate~amplitude (Weissenberg number).~~When the Weissenberg number is large, the elastic liquids respond~with~a shear stress over a series of odd-multiples of the test frequency.~~In this lecture we will explore recent attempts to deepen our understand of the physics of these higher harmonics, including especially harmonics higher than the third. ~ [Preview Abstract] |
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KP1.00107: Flow Characteristics of Lid-Driven Cavities with Particle Suspensions using an Eulerian-Lagrangian Modeling Approach Morakinyo Adesemowo, John Shelton Previous experimental and numerical investigations involving lid-driven cavity flows with particle suspensions have primarily focused on particle tracking and the visualization of complex three-dimensional structures that compose the flow field. However, these particle suspensions and their resulting particle-particle interactions could also be viewed as a system of time-dependent perturbation equations to the steady-state Navier-Stokes equations and could affect both the stability and steady-state characteristics of the two-dimensional lid-driven cavity system. In this investigation, an Eulerian-Lagrangian approach to modeling particle suspensions in the lid-driven cavity is utilized in FV-CFD simulations to investigate the effect particle density, area fraction, and Reynolds number have on the two-dimensional flow characteristics of a laminar fluid. Observations have indicated that the development of the primary vortex in the lid-driven cavity varies according to the area fraction of particle suspensions in the system; transitioning from development via an adverse pressure gradient at the top-right corner of the cavity towards particle-laden behavior where particle-particle interactions dominate the development of the primary vortex. Dynamic responses were also observed for particle systems of less dense particles. Finally, a comparison between flows perturbed using disturbance velocities and from particle interactions was performed. [Preview Abstract] |
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KP1.00108: Interactions between mean flow and turbulence in the 2D condensate Corentin Herbert, Gregory Falkovich, Anna Frishman Understanding the interaction of a mean flow with turbulent fluctuations is a central problem in turbulence theory. Here, we shall tackle this issue in the framework of incompressible 2D turbulence in a finite box. In the presence of small-scale energy injection and small large-scale friction, the inverse cascade of energy leads to a stationary state made of a pair of coherent vortices, upon which incoherent turbulent fluctuations are superimposed. Due to the time scale separation between the mean-flow and turbulence, an asymptotic expansion of the hierarchy of moments can be carried out to obtain closed equations describing both the mean flow and the fluctuations profiles. Using extensive numerical simulations, we will test the validity of these analytical predictions. In particular, we will discuss how the components of the Reynolds stress tensor scale with both distance from vortex core and large scale friction, which is the small parameter in the theory. [Preview Abstract] |
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KP1.00109: Unifying Rules for Aquatic Locomotion Mehdi Saadat, August Domel, Valentina Di Santo, George Lauder, Hossein Haj-Hariri Strouhal number, St ($=$fA/U)$,$ a scaling parameter that relates speed, U, to the tail-beat frequency, f, and tail-beat amplitude, A, has been used many times to describe animal locomotion. It has been observed that swimming animals cruise at 0.2$\le $St$\le $0.4. Using simple dimensional and scaling analyses supported by new experimental evidence of a self-propelled fish-like swimmer, we show that when cruising at minimum hydrodynamic input power, St is predetermined, and is only a function of the shape, i.e. drag coefficient and area. The narrow range for St, 0.2-0.4, has been previously associated with optimal propulsive efficiency. However, St alone is insufficient for deciding optimal motion. We show that hydrodynamic input power (energy usage to propel over a unit distance) in fish locomotion is minimized at all cruising speeds when A$^{\mathrm{\ast }}(=$A/L), a scaling parameter that relates tail-beat amplitude, A, to the length of the swimmer, L, is constrained to a narrow range of 0.15-0.25. Our analysis proposes a constraint on A$^{\mathrm{\ast }}$, in addition to the previously found constraint on St, to fully describe the optimal swimming gait for fast swimmers. A survey of kinematics for dolphin, as well as new data for trout, show that the range of St and A$^{\mathrm{\ast }}$ for fast swimmers indeed are constrained to 0.2-0.4 and 0.15-0.25, respectively. Our findings provide physical explanation as to why fast aquatic swimmers cruise with relatively constant tail-beat amplitude at approximately 20 percent of body length, while their swimming speed is linearly correlated with their tail-beat frequency. [Preview Abstract] |
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KP1.00110: Unsteady adjoint for large eddy simulation of a coupled turbine stator-rotor system Chaitanya Talnikar, Qiqi Wang, Gregory Laskowski Unsteady fluid flow simulations like large eddy simulation are crucial in capturing key physics in turbomachinery applications like separation and wake formation in flow over a turbine vane with a downstream blade. To determine how sensitive the design objectives of the coupled system are to control parameters, an unsteady adjoint is needed. It enables the computation of the gradient of an objective with respect to a large number of inputs in a computationally efficient manner. In this paper we present unsteady adjoint solutions for a coupled turbine stator-rotor system. As the transonic fluid flows over the stator vane, the boundary layer transitions to turbulence. The turbulent wake then impinges on the rotor blades, causing early separation. This coupled system exhibits chaotic dynamics which causes conventional adjoint solutions to diverge exponentially, resulting in the corruption of the sensitivities obtained from the adjoint solutions for long-time simulations. In this presentation, adjoint solutions for aerothermal objectives are obtained through a localized adjoint viscosity injection method which aims to stabilize the adjoint solution and maintain accurate sensitivities. Preliminary results obtained from the supercomputer Mira will be shown in the presentation. [Preview Abstract] |
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KP1.00111: High order discontinuous Galerkin discretizations with discontinuity resolution within the cell John Ekaterinaris, Konstantinos Panourgias The nonlinear filter of Yee et al. and used for low dissipative well-balanced high order accurate finite-difference schemes is adapted to the finite element context of discontinuous Galerkin (DG) discretizations. The performance of the proposed nonlinear filter for DG discretizations is demonstrated for different orders of expansions for one- and multi-dimensional problems with exact solutions. It is shown that for higher order discretizations discontinuity resolution within the cell is achieved and the design order of accuracy is preserved. The filter is applied for inviscid and viscous flow test problems including strong shocks interactions to demonstrate that the proposed dissipative mechanism for DG discretizations yields superior results compared to the results obtained with the TVB limiter and high-order hierarchical limiting [2]. The proposed approach is suitable for p-adaptivity in order to locally enhance resolution of three-dimensional flow simulations. [1] H.C. Yee, N.D. Sandham, M.J. Djomehri, J. Comput. Phys., 150 (1999) 199-238. [2] K. Panourgias, J.A. Ekaterinaris, Comput. Methods Appl. Mech. Engrg., 299 (2016) 254-282. [Preview Abstract] |
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KP1.00112: Simultaneous fingering, double-diffusive convection, and thermal plumes derived from autocatalytic exothermic reaction fronts Matthew W. Eskew, Jason Harrison, Reuben H. Simoyi Oxidation reactions of thiourea by chlorite in a Hele-Shaw cell are excitable, autocatalytic, exothermic, and generate a lateral instability upon being triggered by the autocatalyst. Reagent concentrations used to develop convective instabilities delivered a temperature jump at the wave front of 2.1 K. The reaction zone was 2 mm and due to normal cooling after the wave front, this generated a spike rather than the standard well-studied front propagation. The reaction front has solutal and thermal contributions to density changes that act in opposite directions due to the existence of a positive isothermal density change in the reaction. The competition between these effects generates thermal plumes. The fascinating feature of this system is the coexistence of plumes and fingering in the same solution which alternate in frequency as the front propagates, generating hot and cold spots within the Hele-Shaw cell, and subsequently spatiotemporal inhomogeneities. The small $\Delta$T at the wave front generated thermocapillary convection which competed effectively with thermogravitational forces at low E{\"o}tv{\"o}s Numbers. A simplified reaction-diffusion- convection model was derived for the system. Plume formation is heavily dependent on boundary effects from the cell dimensions. [Preview Abstract] |
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KP1.00113: Number of Packages of Information which are processed in a Second by the Fundamental Particles (strings) of a Human Body Hassan Gholibeigian, Ghasem Gholibeigian, Kazem Gholibeigian The fundamental particle (string) gets a package of complete information of its quantum state via inside of its sub-particle (sub-string) from dimension of information. This package is processed by sub-particle in each Planck time [Gholibeigian, APS 2015, abstract {\#}L1.027]. On the other hand, a 70 kg human's body would have approximately 7*10$^{\mathrm{27}}$~atoms. Of that, 4.7*10$^{\mathrm{27}}$~would be hydrogen atoms. Another 1.8*10$^{\mathrm{27}}$~would be oxygen and there are 7.0*10$^{\mathrm{26}}$~carbon atoms. If we add that all up, total is 2.3*10$^{\mathrm{28}}$ protons, 1.8*10$^{\mathrm{28}}$ neutrons, and 2.3*10$^{\mathrm{28\thinspace \thinspace }}$ electrons. Each proton and neutron has 6 fundamental particles. So the total number of packages of information which are processed by each of us in a second becomes: $I=[6\times (2.3+1.8)\times 10^{28}+2.3\times 10^{28}]\times 10^{44}=2.69\times 10^{73}packages$ The processed information carry by fundamental particles. Based on Shanon equation,$I=-S$, this number can be equal to the increased entropy of each of us per second too. [Preview Abstract] |
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KP1.00114: The Generalized Onsager Model and DSMC Simulations of High-Speed Rotating Flow with Swirling Feed Dr. Sahadev Pradhan The generalized Onsager model for the radial boundary layer and of the generalized Carrier-Maslen model for the axial boundary layer at the end-caps in a high-speed rotating cylinder ((S. Pradhan {\&} V. Kumaran, J. Fluid Mech., 2011, vol. 686, pp. 109-159); (V. Kumaran {\&} S. Pradhan, J. Fluid Mech., 2014, vol. 753, pp. 307-359)), are extended to incorporate the angular momentum of the feed gas for a swirling feed for single component gas and binary gas mixture. For a single component gas, the analytical solutions are obtained for the sixth-order generalized Onsager equations for the master potential, and for the fourth-order generalized Carrier-Maslen equation for the velocity potential. In both cases, the equations are linearized in the perturbation to the base flow, which is a solid-body rotation. The equations are restricted to the limit of high Reynolds number and (length/radius) ratio, but there is no limitation on the stratification parameter. The linear operators in the generalized Onsager and generalized Carrier-Maslen equations with swirling feed are still self-adjoint, and so the eigenfunctions form a complete orthogonal basis set. The analytical solutions are compared with direct simulation Monte Carlo (DSMC) simulations. The comparison reveals that the boundary conditions in the simulations and analysis have to be matched with care. When these precautions are taken, there is excellent agreement between analysis and simulations, to within 15{\%}. [Preview Abstract] |
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KP1.00115: The scaling transition of Nu number and boundary layer thickness in RB convection Hong-Yue Zou, Xi Chen, Zhen-Su She A quantitative theory is developed for the vertical mean temperature profile (MTP) and mean velocity profile (MVP) in turbulent Rayleigh-Benard Convection (RBC), which explains the experimental and numerical observations of logarithmic law in MTP and the Rayleigh number (Ra)-dependence of its coefficient A. The theory extends a symmetry analysis of canonical wall-bounded turbulent flows, which allows to extract accurate Ra scaling of the sub-layer, buffer layer and log-layer thicknesses from the empirical data over a wide range of Ra. In particular, the scaling of the multi-layer thicknesses predicts that the log-law coefficient A follows a -0.121 scaling, which agrees well with the experimental data. More interestingly, a scaling transition is discovered for the kinetic sublayer thickness around Ra of 1010, which yields a scaling transition of Nu from 1/3 to 0.38. We also develop a new explanation for mean temperature logarithmic law: the effect of inverse pressure gradient drives plumes upwards near the side wall, and yields a similarity between temperature and momentum transport in the vertical direction. [Preview Abstract] |
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KP1.00116: An immersed boundary method for two-phase fluids and gels and the swimming of Caenorhabditis elegans through viscoelastic fluids Pilhwa Lee, Charles Wolgemuth While swimming in Newtonian fluids has been examined extensively, only recently have investigations into microorganism swimming through non-Newtonian fluids and gels been explored. The equations that govern these more complex media are often nonlinear and require computational algorithms to study moderate to large amplitude motions of the swimmer. Here we develop an immersed boundary method for handling fluid-structure interactions in a general two-phase medium, where one phase is a Newtonian fluid and the other phase is viscoelastic. We use this algorithm to investigate the swimming of an undulating, filamentary swimmer in 2D. A novel aspect of our method is that it allows one to specify how forces produced by the swimmer are distributed between the two phases of the fluid. The algorithm is validated by comparison to theoretical predictions for small amplitude swimming in gels and viscoelastic fluids. We show how the swimming velocity depends on material parameters of the fluid and the interaction between the fluid and swimmer. In addition, we simulate the swimming of \emph{Caenorhabditis elegans} in viscoelastic fluids and find good agreement between the swimming speeds and fluid flows in our simulations and previous experimental measurements. [Preview Abstract] |
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KP1.00117: Inherently Unstable Internal Gravity Waves Reza Alam Here we show that there exist internal gravity waves that are inherently unstable, that is, they cannot exist in nature for a long time. The instability mechanism is a one-way (irreversible) harmonic-generation resonance that permanently transfers the energy of an internal wave to its higher harmonics. We show that, in fact, there are countably infinite number of such unstable waves. For the harmonic-generation resonance to take place, nonlinear terms in the free surface boundary condition play a pivotal role, and the instability does not obtain for a linearly-stratified fluid if a simplified boundary condition such as rigid lid or linear form is employed. Harmonic-generation resonance discussed here also provides a mechanism for the transfer of the energy of the internal waves to the higher-frequency part of the spectrum where internal waves are more prone to breaking, hence losing energy to turbulence and heat and contributing to oceanic mixing. [Preview Abstract] |
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KP1.00118: Braids in a two-body micro swimming Mehdi Mirzakhanloo, Mir Abbas Jalali, M.-Reza Alam Here we show that microswimmers' trajectories may get entangled as a result of their mutual hydrodynamic interactions, resulting in a group behavior that is significantly different from individual swimmers' trajectories. Specifically, we consider a two-swimmer motion of "Quadroar", a newly proposed swimmer consists of two axles of rotating disks connected through a linear reciprocating actuator. In the absence of hydrodynamic interaction, each microswimmer moves along a straight path. When hydrodynamic interaction is introduced, the two swimmers move along tightly woven trajectories whose properties depend on the swimmers' initial conditions. We also show that if swimmers are sent toward each other they may reach an equilibrium at which while they are swimming (i.e. spending energy) no net motion is achieved. We further discuss that since the streamlines of the flow induced by the Quadroar closely resemble the oscillatory flow field of the green alga Chlamydomonas reinhardtii, our findings can thus be utilized to understand the interactions of microorganisms with each other. [Preview Abstract] |
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KP1.00119: Removal of bio-aerosols by water flow on surfaces in health-care settings Han Yu, Yuguo Li Hand hygiene is one of the most important and efficient measures to prevent infections, however the compliance with hand hygiene remains poor especially for health-care workers.\footnote{World Health Organization. \textbf{WHO Guidelines on Hand Hygiene in Health Care.} 2009}\\To improve this situation, the mechanisms of hand cleansing need to be explored and a detailed study on the adhesion interactions for bio-aerosols on hand surfaces and the process during particles removal by flow is significant for more efficient methods to decrease infections. The first part of presentation will focus on modelling adhesion interactions between particles, like bacteria and virus, and hand surfaces with roughness in water environment. The model presented is based on the DLVO and its extended theories.The removal process comes next, which will put forward a new model to describe the removal of particles by water flow. In this model, molecular dynamics is combined with particle motion and the results by the model will be compared with experiment results and existed models (RnR, Rock \& Roll). Finally, possible improvement of the study and future design of experiments will be discussed. [Preview Abstract] |
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KP1.00120: Prediction of local losses of low Re flows in elastic porous media Sid Becker, Stefan Gasow An isotropic elastic porous structure whose pore scale geometry is regular (periodically uniform) will experience non-uniform deformation when a viscous fluid flows through the matrix under the influence of an externally applied pressure difference. In such a case, the flow field will experience a non uniform pressure gradient whose magnitude increases in the direction of bulk flow. In this study, a method is presented that predicts local losses of the flow through a porous matrix whose geometry varies in the direction of flow. Employing an asymptotic expansion about the deformation provides an expression relating local hydraulic permeability to local pore geometry. In this way the pressure field is able to be determined without requiring the explicit solution of the flow field. In this study a test case is presented showing that the local pressure losses are predicted to be within 0.5{\%} those of the solution to the Navier-Stokes Equations. The approach can be used to simplify the coupled fluid-solid problem of flow through elastic porous media by replacing the need to explicitly solve the flow field. [Preview Abstract] |
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KP1.00121: Experimental study of filament break-off of dense suspensions Gustaf Mårtensson, Fabian Carson As with the jet printing of dyes and other low-viscosity fluids, the jetting of dense fluid suspensions is dependent on the repeatable break-off of the fluid filament into well-formed droplets. It is well known that the break-off of dense suspensions is dependent on the volume fraction of the solid phase, particle size and morphology, fluid phase viscosity et cetera, see for example van Deen et al. (2013). The purpose of this study is to establish a deeper understanding of the break-off process of filaments of dense suspensions. The experimental set-up consists of a filament break-off device (FilBO) developed in-house. The suspension samples consist of a resin-based flux and spherical particles with diameters of \(d_p=10-25 \mu \)m. A cylindrical sample (\( d_{\mathrm{cyl}}=1\) mm and \( h_{\mathrm{cyl}}=1\) mm) of the suspension is extended using a cylindrical probe travelling between \( v_{\mathrm{cyl}}=100-800\) mm/s in the vertical direction. A decrease in particle size correlates with increasing break-off length. Further results relating break-off length and rate versus particle diameter, volume fraction and probe speed will be presented. Comparisons of the filament break-off experiments with practical jetting of the suspensions will be presented. [Preview Abstract] |
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KP1.00122: A Quasi-Dynamic Approach to modelling Hydrodynamic Focusing Aditya Kommajosula, Songzhe Xu, Chueh-Yu Wu, Dino Di Carlo, Baskar Ganapathysubramanian We examine a particle's tendency at different spatial locations to shift/rotate towards the equilibrium location, by constrained simulation. Although studies in the past have used this procedure in conjunction with FSI methods to great effect, the current work in 2D explores an alternative approach by utilizing a modified trust-region-based root-finding algorithm to solve for particle position and velocities at equilibrium, using ``snapshots" of finite-element solutions to the steady-state Navier-Stokes equations iteratively over a computational domain attached to the particle reference frame. Through an assortment of test cases comprising circular and non-circular particle geometries, an incorporation of stability theory as applicable to dynamical systems is demonstrated, to locate the final focusing location and velocities. The results are compared with previous experimental/numerical reports, and found to be in close agreement. A thousand-fold increase is observed in computational time for the current workflow from its transient counterpart, for an illustrative case. The current framework is formulated in 2D for 3 Degrees-of-Freedom, and will be extended to 3D. This framework potentially allows for quick, high-throughput parametric space studies of equilibrium scaling laws. [Preview Abstract] |
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KP1.00123: The Effect of Elasticityon the Extrudate Swell of Molten Polymers. Savvas Hatzikiriakos, Vinod Kumar Konaganti The extrudate swell of an industrial grade high molecular weight high-density polyethylene (HDPE) in capillary dies is studied using the integral K-BKZ constitutive model. The non-linear viscoelastic flow properties of the polymer resin are studied for a broad range of large step shear strains and high shear rates using the cone partitioned plate (CPP) geometry of the stress/strain controlled rotational rheometer. This allowed the determination of the rheological parameters accurately, in particular the damping function, which is proven to be the most important in simulating transient flows such as extrudate swell. A series of simulations performed using the integral K-BKZ Wagner model with different values of the Wagner exponent $n$, ranging from $n=$0.15 to 0.5, demonstrates that the extrudate swell predictions are extremely sensitive to the Wagner damping function exponent. Using the correct $n-$value resulted in extrudate swell predictions that are in excellent agreement with experimental measurements. . [Preview Abstract] |
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KP1.00124: Performance of a reduced-order FSI model for flow-induced vocal fold vibration Siyuan Chang, Haoxiang Luo Vocal fold vibration during speech production involves a three-dimensional unsteady glottal jet flow and three-dimensional nonlinear tissue mechanics. A full 3D fluid-structure interaction (FSI) model is computationally expensive even though it provides most accurate information about the system. On the other hand, an efficient reduced-order FSI model is useful for fast simulation and analysis of the vocal fold dynamics, which is often needed in procedures such as optimization and parameter estimation. In this work, we study the performance of a reduced-order model as compared with the corresponding full 3D model in terms of its accuracy in predicting the vibration frequency and deformation mode. In the reduced-order model, we use a 1D flow model coupled with a 3D tissue model. Two different hyperelastic tissue behaviors are assumed. In addition, the vocal fold thickness and subglottal pressure are varied for systematic comparison. The result shows that the reduced-order model provides consistent predictions as the full 3D model across different tissue material assumptions and subglottal pressures. However, the vocal fold thickness has most effect on the model accuracy, especially when the vocal fold is thin. [Preview Abstract] |
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KP1.00125: Bringing first-hand experience one step closer to theoretical understanding Haoxiang Luo, Mike Myers Many theoretical concepts and analytical approaches in fluid mechanics are challenging to teach. Classroom demos are very useful to engage and motivate students, but they do not necessarily lead straightforwardly to higher level understanding of model abstraction that is expressed with mathematical equations. To facilitate the process, we have designed a few demos and integrated them with quantitative measurements and theoretical analysis. These demos, usually generated from daily life examples, are of low cost and simple to implement, and the experimental procedures do not take significant time in a 50-min lecture. When combining them with classroom interactions, problem solving, and discussions, we found that these modules are effective in helping students in the learning process. [Preview Abstract] |
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KP1.00126: Electrorotation instability of a liquid bridge Gerardo Pradillo, Petia Vlahovska We experimentally study the behavior of an oil droplet sandwiched between two ITO coated glass electrodes in a DC electric field. Above a threshold electric field, the contact line contour changes from circular to a steady flower-like one. As the field strength increases, the wave becomes unsteady and begins to rotate. It is observed that the stable mode of the wavy contact line is different if the field is applied as a pulse or gradually increased in small steps, which suggests that the charge relaxation time is important. The amplitude of the wave is related to the conductivity of the drop fluid, which is controlled by adding organic electrolytes. The physical mechanism of the instability is yet to be explained. [Preview Abstract] |
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KP1.00127: Tunable Superomniphobic Surfaces for Sorting Droplets by Surface Tension Sanli Movafaghi, Wei Wang, Ari Metzger, Desiree Williams, John Williams, Arun Kota Manipulation of liquid droplets on super-repellent surfaces (i.e., surfaces that are extremely repellent to liquids) has been widely studied because droplets exhibit high mobility on these surfaces due to the ultra-low adhesion, which leads to minimal sample loss and contamination. Although droplet manipulation has been demonstrated using electric fields, magnetic fields, guiding tracks and wettability gradients, to the best of our knowledge, there are no reports of droplet manipulation methods that can sort droplets by surface tension on super-repellent surfaces. In this work, we utilized tunable superomniphobic surfaces (i.e., surfaces that are extremely repellent to virtually all liquids) to develop a simple device with precisely tailored solid surface energy domains that, for the first time, can sort droplets by surface tension. Droplet sorting occurs on our device entirely due to a balance between the work done by gravity and the work expended due to adhesion, without the need for any external energy input. Our device can be fabricated easily in a short time and is particularly useful for in-the-field and on-the-go operations, where complex analysis equipment is unavailable. We envision that our methodology for droplet sorting will enable inexpensive and energy-efficient analytical devices for personalized point-of-care diagnostic platforms and lab-on-a-chip systems. [Preview Abstract] |
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KP1.00128: Free-standing, Flexible Superomniphobic Films Hamed Vahabi, Wei Wang, Sanli Movafaghi, Arun K.Kota Fabrication of most superomniphobic surfaces requires complex process conditions or specialized and expensive equipment or skilled personnel. In order to circumvent these issues and make them end-user friendly, we developed the free-standing, flexible superomniphobic films. These films can be stored and delivered to the end-users, who can readily attach them to virtually any surface (even irregular shapes) and impart superomniphobicity. The hierarchical structure, the re-entrant texture and the low solid surface energy render our films superomniphobic for a wide variety of liquids. We demonstrate that our free-standing, flexible, superomniphobic films have applications in enhanced chemical resistance and enhanced weight bearing. [Preview Abstract] |
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KP1.00129: Effect of Fluid Structure Interaction on the Wake Structure of a Thin Flexible Cylinder Harika Gurram, Chelakara Subramanian, Priyanka Kanherkar Previous studies by the authors of the drag coefficient for thin flexible cylinders (diameter \textasciitilde O(mm)) in a cross flow for Reynolds's numbers range between 100-1000 showed about 20 -- 30 percent reduction compared to literature values. At free stream low Reynolds number around 100 the spectral analysis of the hotwire signals in the wake showed tonal and broadband frequencies suggesting features similar to transition flows. To better understand the flow behind the cylinder and wake structure interaction with boundary layer for above range of Reynolds number DNS simulations were conducted. The computational study is performed for two cases: (1) flow on rigid thin cylinder, and (2) flow with 3-D fluid structure interaction for the thin cylinder. It is observed the coefficient of drag values computed for the rigid wire were 8 -12 percent lower compared to the experimental results, while simulation with the fluid structure interaction gave results within 4 percent of the experimental values. The wake structure results based on the experiment and computational study will be discussed. [Preview Abstract] |
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KP1.00130: Nonlinear Acoustics at the Air-Water Free Surface Seth Pree, Brian Naranjo, Seth Putterman According to linear acoustics, airborne sound incident on a water surface transmits only a tenth of a percent of its energy. This difficulty of transmitting energy across the water surface limits the feasibility of standoff ultrasound imaging. We propose to overcome this long standing problem by developing new methods of coupling into the medium at standoff. In particular, we believe that the acoustic nonlinearity of both the air and the medium may yield a range of effects in the vicinity of the surface permitting an efficient transmission of ultrasound from the air into the medium. The recent commercial availability of parametric speakers that deliver modulated 100kHz ultrasound at 135dB to nonlinearly generate music at 95dB provides an interesting platform with which to revisit the transmission of sound across acoustic impedance mismatches. We show results of experimental studies of the behavior of the air-water free surface when subjected to large amplitude acoustic pressures from the air. [Preview Abstract] |
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KP1.00131: Effect of angle of attack on the flow past a harbor seal vibrissa shaped cylinder Hyo Ju Kim, Hyun Sik Yoon The present study considered the geometric disturbance inspired by a harbor seal vibrissa of which undulated surface structures are known as a detecting device to capture the water movement induced by prey fish. In addition, this vibrissa plays an important role to suppress vortex-induced vibration, which has been reported by the previous researches. The present study aims at finding the effect of the angle of attack (AOA) on flow characteristics around the harbor seal vibrissa shaped cylinder, since the flow direction facing the harbor seal vibrissa with the elliptic shape can be changed during the harbor seal's movements and surrounding conditions. Therefore, we considered a wide range of AOA varying from 0 to 90 degree. We carried out large eddy simulation (LES) to investigate the flow around inclined vibrissa shaped cylinder for the Reynolds number (Re) of 500 based hydraulic diameter of a harbor seal vibrissa shape. For comparison, the flow over the elliptic cylinder was also simulated according to AOA at the same Re. The vortical structures of both vibrissa shaped and elliptic cylinders have been compared to identify the fundamental mechanism making the difference flow quantities. [Preview Abstract] |
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KP1.00132: Elasticity-Driven Backflow of Fluid-Driven Cracks Ching-Yao Lai, Zhong Zheng, Emilie Dressaire, Guy Ramon, Herbert E. Huppert, Howard A. Stone Fluid-driven cracks are generated by the injection of pressurized fluid into an elastic medium. Once the injection pressure is released, the crack closes up due to elasticity and the fluid in the crack drains out of the crack through an outlet, which we refer to as backflow. We experimentally study the effects of crack size, elasticity of the matrix, and fluid viscosity on the backflow dynamics. During backflow, the volume of liquid remaining in the crack as a function of time exhibits a transition from a fast decay at early times to a power law behavior at late times. Our results at late times can be explained by scaling arguments balancing elastic and viscous stresses in the crack. This work may relate to the environmental issue of flowback in hydraulic fracturing. [Preview Abstract] |
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KP1.00133: Time-Reversal of Nonlinear Water Waves Amin Chabchoub, Guillaume Ducrozet, Mathias Fink Time-reversal (TR) refocusing of hydrodynamic nonlinear waves can be discussed within the framework of the nonlinear Schr\"{o}dinger equation (NLS). Indeed, exact solutions of the latter weakly nonlinear evolution equation can be used to study the applicability and limitations of wave refocusing using TR mirrors in hydrodynamics. Recent laboratory experiments confirmed the applicability of TR approach to breathers, known to model extreme and doubly-localized wave configurations. In order to study the range of validity of the TR approach to nonlinear waves, a numerical study using a unidirectional numerical water wave tank, implemented by the higher-order spectral method, reveals new insights to the problem. The validity of the TR approach is assessed over a diversity of NLS configurations, ranging from stationary envelope and breathing solutions, pointing out the importance of higher-order dispersive and particularly nonlinear effects in the refocusing of these hydrodynamic localized structures. Due to the interdisciplinary nature of the approach several applications in other nonlinear dispersive physical media may result in addition to evident usage in the field of ocean engineering. [Preview Abstract] |
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KP1.00134: Reducing spin-up time for DNS and LES of turbulent channel flow Kurt Nelson, Oliver Fringer In DNS or LES of turbulent channel flow, significant computational resources are wasted on simulation of flow evolution as it approaches statistical equilibrium. Although the driving pressure gradient that produces the desired time-averaged bottom stress is known a-priori, during flow spin-up this pressure gradient is typically not in balance with the time-averaged bottom stress, leading to flow acceleration beyond the target velocity which can significantly prolong the time to reach statistical equilibrium. Through DNS of turbulent channel flow with Re$_{\mathrm{\tau }}=$500, we present a method that ensures a time invariant volume-averaged streamwise velocity. While the method eliminates spin-up time related to approaching the target volume-averaged velocity, spin-up time is still needed for the turbulence to reach statistical equilibrium. To this end, we study the evolution of the turbulence in response to different initial velocity profiles and initial random perturbations and show that initialization with a laminar velocity profile significantly reduces spin-up time because the linear distribution of vertical shear triggers turbulence faster than it would with a log-law velocity profile. [Preview Abstract] |
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KP1.00135: An engineering closure for heavily under-resolved coarse-grid CFD in large applications Andreas G Class, Fujiang Yu, Thomas Jordan Even though high performance computation allows very detailed description of a wide range of scales in scientific computations, engineering simulations used for design studies commonly merely resolve the large scales thus speeding up simulation time. The coarse-grid CFD (CGCFD) methodology is developed for flows with repeated flow patterns as often observed in heat exchangers or porous structures. It is proposed to use inviscid Euler equations on a very coarse numerical mesh. This coarse mesh needs not to conform to the geometry in all details. To reinstall physics on all smaller scales cheap subgrid models are employed. Subgrid models are systematically constructed by analyzing well-resolved generic representative simulations. By varying the flow conditions in these simulations correlations are obtained. These comprehend for each individual coarse mesh cell a volume force vector and volume porosity. Moreover, for all vertices, surface porosities are derived. CGCFD is related to the immersed boundary method as both exploit volume forces and non-body conformal meshes. Yet, CGCFD differs with respect to the coarser mesh and the use of Euler equations. We will describe the methodology based on a simple test case and the application of the method to a 127 pin wire-wrap fuel bundle. [Preview Abstract] |
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KP1.00136: Pulling rigid bodies through granular material Ryan Kubik, Emilie Dressaire The need for anchoring systems in granular materials such as sand is present in the marine transportation industry, e.g. to layout moorings, keep vessels and docks fixed in bodies of water, build oil rigs, etc. The holding power of an anchor is associated with the force exerted by the granular media. Empirical evidence indicates that the holding power depends on the size and shape of the anchoring structure. In this model study, we use a two-dimensional geometry in which a rigid body is pulled through a granular media at constant velocity to determine the drag and lift forces exerted by a granular medium on a moving object. The method allows measuring the drag force and recording the trajectory of the rigid object through the sand. We systematically vary the size and geometry of the rigid body, the properties of the granular medium and the extraction speed. For different initial positions of a cylindrical object pulled horizontally through the medium, we record large variations in magnitude of the drag and a significant lift force that pulls the object out of the sand. [Preview Abstract] |
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KP1.00137: Similarity Solution for High Weissenberg Number Flow of Upper-Convected Maxwell Fluid on a Linearly Stretching Sheet nariman ashrafi, Meysam Mohamadali High Weissenberg boundary layer flow of viscoelastic fluids on a stretching surface has been studied. The flow is considered to be steady, low inertial, and two-dimensional. Upon proper scaling and by means of an exact similarity transformation, the nonlinear momentum and constitutive equations of each layer transform into the respective system of highly nonlinear and coupled ordinary differential equations. Numerical solutions to the resulting boundary value problem are obtained using an efficient shooting technique in conjunction with a variable stepping method for different values of pressure gradients. It is observed that, unlike the Newtonian flows, in order to maintain a potential flow, normal stresses must inevitably develop. The velocity field and stresses distributions over plate are presented for difference values of pressure gradient and Weissenberg numbers. [Preview Abstract] |
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KP1.00138: Viscoelastic Squeeze Flow nariman ashrafi, Mehdi Shafahi The squeeze flow of a nonlinear viscoelastic flow is studied. In particular the flow of an upper-convected Maxwell fluid between two approaching disks of is analyzed. The momentum and continuity equations together with constitutive relations are solved by a low-order method. Both no slip and slip boundary conditions are considered. Next, stress components are evaluated and flow stability is investigated. It is observed that as the disks approach velocity is increased the developed stresses, which are interrelated to velocity gradients through the constitutive relation, are altered exponentially. This analysis is applicable to many industrial instances of such as lubrication as well as natural joints. [Preview Abstract] |
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