Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session 1B: Poster Session (6:15PM- 7:00PM) |
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Room: Spirit of Pittsburgh Gallery |
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1B.00001: ACOUSTICS |
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1B.00002: Design of an Acoustic Array for Comparison with an Alternative Source Localization Method Deshawn Coombs, Jacques Lewalle, Mark Glauser, Guannan Wang We report on the design, testing and construction of a conventional acoustic array, and document an alternate method of signal processing. The purpose of the new algorithm is to improve the spatial localization of acoustic sources. The reference results are obtained using the beamforming algorithm. The array design includes 60 microphones with a maximum aperture diameter of 39 inches. The arrays target frequency range is 500-5000 Hz. The new algorithm uses fewer microphones. We will show results with simulated signals and with jet noise experimental data. Details of the array calibration and representative data from measurements will be presented along with data post-processing procedures. [Preview Abstract] |
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1B.00003: AERODYNAMICS |
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1B.00004: Vortex Generation by a Low-Camber Rotating Arc Wing Majid Molki A rotating circular-arc wing is placed in a uniform turbulent flow to generate and study vortices. The momentum equation is modified for the non-inertial rotating reference frame attached to the wing. Turbulence is modeled by the $k-\omega$ SST model. Using the open-source software OpenFOAM, the conservation equations are solved on a dynamic mesh which rotates with the wing, and the flow is resolved all the way to the wall. The computations are performed for Re = 60,000 with rotation number ranging from Ro = 0 to 0.2. Lift and drag coefficients, contours of vorticity and streamlines, and pressure and vorticity over the wing are presented. The relationship between wall vorticity, pressure gradient, and vorticity flux is considered. This study indicates that rotation of the wing creates a dynamic situation that delays the stall to higher angles of attack and enhances the lift and drag coefficients. Depending on the orientation of the wing and rotational speed, a variety of flow patterns appear which include the leading-edge and rolling vortices, dynamic stall, vortex sheets, and stretching and bending of vortex sheets. The relationship between vorticity and pressure gradients are utilized to interpret and explain the flow features. [Preview Abstract] |
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1B.00005: BIOFLUIDS . [Preview Abstract] |
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1B.00006: Low-Reynolds-number swimming near a wall Gaojin Li, Arezoo Ardekani Hydrodynamics of swimming organisms in a low Reynolds number regime near a no-slip wall has been a subject of growing interest in recent years because of its importance in many health and environmental problems. In addition to the changes in the swimming speed and energy expenditure of organisms in the presence of a wall, unexpected interesting swimming dynamics has been reported in recent experiments. In this study, the hydrodynamics of an archetypal low-Reynolds number swimmer, called ``squirmers,'' near a wall has been numerically studied. Depending on the swimming mechanism and swimming direction, three different modes are distinguished: (a) squirmer escaping from the wall, (b) squirmer swimming along the wall keeping a constant height and orientation angle and (c) squirmer swimming near the wall in a periodic trajectory. [Preview Abstract] |
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1B.00007: Simulations of the burst and coast swimming behavior of fish Quan Zhou, Keith Moored, Alexander Smits An investigation into the burst and coast swimming behavior of fish is simulated with a 2-D, inviscid Boundary Element Method. The fish is modeled as a thin pitching panel that is allowed to free swim. A simple drag model is used where drag is proportional to the velocity squared in order to calculate the cruising velocity. The burst-coast behavior is modeled by a coasting phase, where the panel is motionless, and a burst phase, where the panel pitches with a single sine wave motion. Varying the frequency of the fin-beat and the duration of the duty cycle (the ratio of the burst-phase to the entire period), it is found that it is possible to alter swimming motion to yield a decrease of 50\% in the cost of transport with no sacrifice of time-averaged cruising velocity. The analyses of the wake structure demonstrate how vortices shed by the fish affect and shape swimming dynamics. [Preview Abstract] |
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1B.00008: Reduction of Urinary Tract Infections Caused By Urethral Catheter through the Implementation of Hydrophobic Coating and Geometrical Modifications Aya Gare Catheter-Associated Urinary Tract Infection (CAUTI) is the most common nosocomial infection in the U.S. healthcare system. The obstruction of urine caused by confined air bubbles result in the development of urinary back-flow and stagnation, wherein microbial pathogens could multiply rapidly and colonization within catheters become commonplace. Infections can be prevented by aseptic insertion and the maintenance of a closed drainage system, keeping high infection control standards, and preventing back-flow from the catheter bag. The goal of this study is to assess the effectiveness of a simple, low cost, modification that may be implemented into current catheter designs to reduce the incidence of CAUTI. Using the principle of transmission of fluid-pressure and the Young-Laplace equation for capillary pressure difference, this research focuses on improving the liquid flow in the presence of confined bubbles to prevent stagnation and reflux of bacteria-ridden urine into the body. Preliminary experiments are performed on a variety of tubes with hydrophobic-coating the interior, as well as geometrically modifying the tubes. Proof-of-Concept Prototype tubes are used to represent the drainage system of the catheter structure. [Preview Abstract] |
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1B.00009: Dynamics of Surfactant Liquid Plugs at Bifurcating Lung Airway Models Hossein Tavana A surfactant liquid plug forms in the trachea during surfactant replacement therapy (SRT) of premature babies. Under air pressure, the plug propagates downstream and continuously divides into smaller daughter plugs at continuously branching lung airways. Propagating plugs deposit a thin film on airway walls to reduce surface tension and facilitate breathing. The effectiveness of SRT greatly depends on the final distribution of instilled surfactant within airways. To understand this process, we investigate dynamics of splitting of surfactant plugs in engineered bifurcating airway models. A liquid plug is instilled in the parent tube to propagate and split at the bifurcation. A split ratio, R, is defined as the ratio of daughter plug lengths in the top and bottom daughter airway tubes and studied as a function of the 3D orientation of airways and different flow conditions. For a given Capillary number (\textit{Ca}), orienting airways farther away from a horizontal position reduced $R$ due to the flow of a larger volume into the gravitationally favored daughter airway. At each orientation, $R$ increased with 0.0005 \textless\ \textit{Ca} \textless\ 0.05. This effect diminished by decrease in airways diameter. This approach will help elucidate surfactant distribution in airways and develop effective SRT strategies. [Preview Abstract] |
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1B.00010: Computational analysis of wake structure and body forces on marine animal research tag Matthew Rosanio, Jacob Morrida, Melissa Green The Acousounde 3B marine animal research tag is used to study the relationship between the sounds made by whales and their behaviors, and ultimately to improve whale conservation efforts. In practical implementation, some researchers have attached external GPS Fastloc devices to the top surface of the tag, in order to accurately record the position of the whales throughout the deployment. There is a need to characterize the flow over the tag in order to better understand the body forces being exerted on it and how wake turbulence could affect noise measurements. The addition of the GPS Fastloc exacerbates both of these concerns, as it complicates the hydrodynamics of the device. Using CFD techniques, we were able to simulate the flow over the tag with a GPS attachment at multiple yaw angles. We used Pointwise to construct the mesh and Fluent to simulate the flow. We have also used flow visualization to experimentally validate our computational results. It was found that the GPS has a minimal effect on the wake of the tag at a 0 degree offset from the freestream flow. However, at increasing offset angles, the presence of the GPS greatly increased the amount of wake turbulence observed. [Preview Abstract] |
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1B.00011: Physics of Dielectrophoretic Trap by Analogy with Electrophoretic Paul Trap Jae Hyun Park Dielectrophoresis (DEP) is defined as the motion of suspended particles in solvent resulting from polarization forces induced by an inhomogeneous electric field. DEP has been utilized for various biological applications such as trapping, sorting, separation of cells, viruses, nanoparticles, etc. The analysis of DEP trap has been so far based on the period-averaged pondermotive forces only while the dynamic features of DEP trapping have not been attracted. However, the recent study about aqueous electrophoretic Paul trap showed that a close relation between particle properties and their random motions, which cannot be understood via pondermotive effects. Similar to this, the present study reveals a detailed understanding of dynamic responses of DEP trap and their relation to various system parameters. The analogy with electrophoretic Paul trap is emphasized. [Preview Abstract] |
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1B.00012: BUBBLES |
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1B.00013: Saturation of the Afterbounce Shape Instability in Single Bubble Sonoluminescence; Theory and Experiment Mogens Levinsen Excitation of the afterbounce instability represents one route to bubble death in single-bubble sonoluminescence. By taking the existing first order theory for excitation of shape instabilities represented by expansion in a spherical harmonic to second order thereby mixing spherical harmonics of different orders, we show that the exponential growth into bubble disruption in a certain parameter regime is checked and a saturated stable state of shape distortion is possible. Experimental evidence provided by Mie scattering is presented and a possible connection to simultaneous spatially anisotropic light emission discussed. [Preview Abstract] |
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1B.00014: COMPUTATIONAL FLUID DYNAMICS |
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1B.00015: Large Eddy Simulation of a turbulent flow in two dimensional dunes using an immersed boundary method Getnet Agegnehu, Heather D. Smith The flow over dunes separates at the crest, generating a shear layer which has a big role for energy dissipation and formation of coherent structures. Large Eddy Simulations using bodyfitted and immersed boundary grids are performed to study the detailed flow dynamics that occurs in a fixed two dimensional dunes. We used a three-dimensional, non-hydrostatic solver; OpenFOAM for this study. The immersed boundary method was implemented using a discrete forcing approach with direct imposition of the boundary conditions. A periodic boundary condition is imposed in both the streamwise and spanwise directions. No-slip and free slip conditions are applied for the bottom and top walls respectively. The flow is forced with a pressure gradient which yields the mean velocity. The numerical results have been quantitatively compared with an experimental data for the mean flow and turbulence profiles. Resolved streamwise velocity profiles from both the immersed boundary and bodyfitted grids are in a good agreement with the experimental data. A good correlation of turbulent intensities and instantaneous flow fields are also observed between the two methods. It is also shown that the numerical model overestimates the vertical velocity profiles in the leeward side of the dune. [Preview Abstract] |
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1B.00016: A Brownian dynamics simulation of a colloidal particle in an alternating electric field very near an electrode Lei Wang, Dennis Prieve In previous experiments, a single 6 $\mu $m sphere, immersed in a 0.15 mol/m$^{\mathrm{3}}$ electrolyte solution, was put in an alternating electric field (6 kV/m, 100 Hz to 10 kHz) acting normal to a nearby planar electrode. Even in the absence of the applied field, the particle is confined by a potential energy well formed by gravitational attraction and double-layer repulsion. While monitoring the elevation of the particle (order of 300 nm) with Total Internal Reflection Microscopy at millisecond intervals and with the AC field, the particle was observed to experience a steady attraction to the electrode, even when the deterministic oscillations were imperceptibly small. While dielectrophoresis could produce a steady attraction, the observed attraction has a frequency dependence which is not consistent with this force. In this work, we use Brownian dynamics simulation to explore the role of several nonlinearities in the equation of motion: 1) a position-dependent drag coefficient, 2) a position-dependent oscillating force and 3) a non-parabolic shape for the confining potential energy profile (non-linear spring). [Preview Abstract] |
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1B.00017: CONVECTION AND BUOYANCY-DRIVEN FLOWS |
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1B.00018: Rayleigh-Taylor instability: An initial condition study Tom Finn, Sarat chandra Kuchibhatla, Devesh Ranjan The Water Channel facility at Texas A{\&}M University was employed to study the effects of initial conditions on Rayleigh-Taylor instability. Different stages of evolution of the unstable stratification of hot and cold water streams are experimentally recorded using planar imaging techniques and thermocouples. The Atwood number corresponding to a low temperature difference of 7-8 degrees C lies within the range of 0.001-0.002. Repeatable and controllable multimodal initial conditions of up to 11 modes are generated using a flapper mechanism. Dependence of flow behavior on initial wavelength and phase angle are deduced by using sets of experimental cases. Integral mixing width, molecular mixing between the water streams and fine scale mixing of scalars are studied using Planar Laser Imaging Fluorescence, (PLIF) technique. Dependence of these variables on initial condition and their behavior at late times is studied. Anisotropy in the flow field is currently being studied using Particle Image Velocimetry. [Preview Abstract] |
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1B.00019: Two-Way Natural Convection of Divided Statically Unstable Fluid Layers Through Small Openings Christia Tsai The diffusion and convection occurring between a liquid interfaces is studied extensively by many researchers, but the natural convection of unstable fluid layers through small openings has received little attention. The subject could be important in the study of leaking oil or oil release on the sea bed. The diffusion and convection across the liquid interface are studied using flow visualization techniques in conjunction with high speed photography to elucidate this particular fluid mechanics of natural convection occurring unstably. A two-way natural convection occurs in which vertical density stratification is exhibited on both top and bottom layers. In addition to the density stratification, a horizontal density gradient is formed, resulting in an internal wave near the bottom of the tank. Both single opening and multiple openings are investigated. The interactions between multiple openings are revealed. For future study, measurement and micro-beads will be added to the experiment for more detail observation. Two-way natural convection through small opening has potentials in many directions of study upon varies instabilities observed in this experiment. [Preview Abstract] |
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1B.00020: DROPS |
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1B.00021: Investigation of interfacial phenomena and thermocapillary effect on drop evaporation in reduced gravity condition JingChang Xie, Hai Lin Based on ground-based experiments, a drop evaporation experiment will fly aboard Chinese recoverable satellite in the near future This experiment will focus on the interfacial phenomena of phase chance, heat and mass transfer and the effect of thermocapillary convection on drop evaporation process Close attention will also be paid to the contact angle behavior, the triple line shifting and their relations Our ground-based experiments observed the interior flow field and the gaseous exterior of small suspended evaporating drops, the temperature distributions inside and outside the drops. Both good heat conductor and heat insulating material were used as substrate materials to investigate their influence on heat transfer and surface temperature distribution of an evaporating drop Experimental results indicate that for a drop evaporating in ambient temperature without substrate heating, temperature gradients existed along the drop surface which results in stable thermocapillary convection and cells appeared near the surface throughout entire evaporating process. The thermocapillary convection greatly changed drop's interior temperature distribution and the way of energy and mass transfer. Temperature jump or discontinuity was also measured at drop free surface. [Preview Abstract] |
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1B.00022: Size distribution of spray droplets at different temperature Ildoo Kim, Hyung Ju Lee, Ho Jin Choi, Ki-Young Hwang Atomization of a liquid jet through an injection nozzle is not only of fundamental interests but also crucial to many real-life applications like engines, ink-jet printers, flow cytometry. Because of practical importance, there have been many studies on the atomization mechanism such as its dependence on the nozzle shape, ambient air pressure and etc. In this study, we investigate the atomization characteristics focused on its dependence on fluid temperature. We varied the temperature of the fluid from -30 $^{\circ}$C to 300 $^{\circ}$C, and it is injected through a nozzle pneumatically. Such cold or hot jet of fluid is atomized in the flow-controlled chamber, and the size distribution of the spray droplets was measured by optical technique. [Preview Abstract] |
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1B.00023: Droplet motion driven by electro-elasto-capillary effects Jaymeen Shah, Xin Yang, Ying Sun The motion of droplets on natural and synthetic fibers underlines many technological applications including flexible displays, insulation, and smart filters. However, there is a lack of fundamental understanding of the coupled electrical, elastic, and capillary forces on droplets in fiber networks. In the present study, the motion of a water droplet suspended between two electrically insulated fibers of different Young's modulus, lengths and diameters are examined under electric fields. The results on rigid fibers reveal a critical voltage, under which the droplet remain stationary. Above this critical voltage, droplet self-propulsion is observed as a result of the interplay of electro, elasto and capillary forces on the droplet. The effects of the inter-fiber distance and Young's modulus on droplet motion are also discussed. The controllable motion of droplets can be used to manipulate or transport liquid at small scales. [Preview Abstract] |
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1B.00024: Stable Drop Formation and Deposition Control in Ink Jet Printing of Polyvinylidene Fluoride Solution Nathaniel Thorne, Xin Yang, Ying Sun Using inkjet printing as an additive fabrication method is an enabling technology for low-cost, high-throughput production of flexible electronics and photonics. Polymeric materials, such as Polyvinylidene fluoride (PVDF), are widely used as dielectric materials for microelectronics, batteries, among others.~ However, due to its large molecular weight and incompatibility with moisture in air, the stable drop formation of PVDF solution is quite challenging. In this study, we examine the effects of solute concentration, nozzle back pressure, ejection waveform, and ambient moisture on the formation of PVDF droplets. The deposition dynamics of inkjet-printed PVDF solutions are then examined as a function of the solvent concentration. Bi-solvents of different surface tensions and vapor pressures are used to induce Marangoni flows in order to suppress the coffee-ring effect. The deposition of a single droplet and the interactions between multiple drops are examined for a better control of the deposition uniformity. Printing of lines and patterns with reduced instability is also discussed. [Preview Abstract] |
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1B.00025: Evolution of vapor into a Leidenfrost layer during drop impact Sang Jun Lee, Ji San Lee, Namseop Kwon, Byung Mook Weon, Kamel Fezzaa, Jung Ho Je When a liquid drop impacts a solid surface heated above the Leidenfrost temperature, the drop rebounds, known as Leidenfrost effect. This phenomenon plays an important role in many cooling and transfer processes involved in fuel combustion or spray cooling. In this study, we investigated the evolution of vapor into a Leidenfrost layer during drop impact using ultrafast X-ray phase-contrast imaging that allowed us to directly visualize the dynamic profiles of drop impact at 150 -- 550C. Initially, we find that nucleation of vapor occurs during drop spreading, forming vapor bubbles. We then reveal that vapor bubbles collapse on the solid surface during drop recoiling, contributing to the formation of a Leidenfrost layer. Furthermore, we studied the effects of temperature and impact velocity on the bouncing dynamics of the drop. [Preview Abstract] |
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1B.00026: FLOW CONTROL |
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1B.00027: Investigation of Flow around Cylinder with Parallel Slit in a Circular Pipe using Flow Visualization Approach Arumuru Venugopal, Lavish Ordia, Amit Agrawal, S.V. Prabhu Flow visualization experiments behind a cylinder with parallel slit placed inside a circular pipe are carried out with water as the working medium. Dye injection technique is employed to visualize the complex vortex formation mechanism behind the bluff bodies. Various wake parameters like Strouhal Number, wake width and the Vortex formation length are calculated from the recorded images with the help of commercial software MATLAB. Three different slit widths with s/d values of 0.1, 0.2 and 0.4 were chosen to study the effect on vortex formation mechanism and the corresponding wake parameters. The dual body character is expected to creep in at higher slit widths. Vortex formation both from the outer and the inner surfaces is observed. Symmetric vortex formation from the outer surface is observed. A separation bubble from each of the inner surface is formed that detaches itself from the bluff body to form a vortex at higher Reynolds. The separation bubble is sensitive to disturbance which is observed in the changing biasness on either side which also results in the transition from symmetric to alternate primary vortices. Their interaction with the outer vortices is observed to effect the strength of the outer primary vortices. [Preview Abstract] |
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1B.00028: GENERAL FLUID DYNAMICS |
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1B.00029: Modulation of flow field due to near-bank roots in small rivers Christian Frias, Jorge Abad, Eddy Langendoen It is well known that the presence of vegetation or log jams decreases the bank shear stress exerted by the water on a river. This fact is used in river restoration to design bank erosion control structures such as engineered log jams or streambank revegetation zones. Also it has been observed in small rivers the presence of exposed near-bank roots and rootwads that could have a similar effect as riparian vegetation or log jams. However, the role of them on the modulation of river bank erosion and sediment transport is still not well understood. An exposed root in the river does not only modify the averaged shear stress or the averaged velocities on the flow field but it changes the instantaneous hydrodynamics too. Thus, it is expected that a root or rootwad produce turbulence coherent structures in the flow field. The analysis of these turbulence coherent structures will give a better insight of the relationship between rootwads geometry and flow field modulation because of them. Herein it is presented a Large Eddy Simulation (LES) of an exposed rootwad at selected small creek in Pennsylvania. The geometry of the rootwad was measured with a terrestrial LiDAR system. The results will be used to characterize the flow field turbulence and associate it to the bank erosion. [Preview Abstract] |
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1B.00030: Performance test of a low cost roof-mounted wind turbine Bernardo Figueroa-Espinoza, Roberto Quintal, Cl\'ement Gouriou, Alicia Aguilar A low cost wind turbine was implemented based on the ideas put forward by Hugh Piggot in his book ``A wind turbine recipe book,'' where such device is developed using materials and manufacturing processes available (as much as possible) in developing countries or isolated communities. The wind turbine is to be mounted on a two stories building roof in a coastal zone of Mexico. The velocity profiles and turbulence intensities for typical wind conditions on top of the building roof were analyzed using numerical simulations (RANS) in order to locate the turbine hub above any recirculation and near the maximum average speed. The coefficient of performance is going to be evaluated experimentally by measuring the electrical power generation and wind characteristics that drive the wind turbine on the field. These experimental results will be applied on the improvement of the wind turbine design, as well as the validation of a numerical simulation model that couples the wind characteristics obtained through CFD with the Blade Element Method (BEM) and an electro-mechanical model of the turbine-shaft-generator ensemble. [Preview Abstract] |
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1B.00031: Flow past 2-D Hemispherical Rigid Canopies Maria-Isabel Carnasciali The flow past a 2-dimensional rigid hemispherical shape is investigated using PIV. Flow field measurements and images were generated with the use of a Thermoflow{\textregistered} apparatus. Results of this study are compared to prior work (APS DFD 2012 Session E9.00003) which employed CFD to investigate the flow in the near wake of hemispherical parachutes. The various sized gaps/open areas were positioned at distinct locations. The work presented here is part of a larger research project to investigate flow fields in deceleration devices and parachutes. Understanding the pitch-stability of parachutes is essential for accurate design and implementation of these deceleration devices but they present a difficult system to analyze. The flexibility of the parachute fabric results in large variations in the parachute geometry leading to complex fluid-structure interactions. Such flow, combined with flow through gaps and open areas, has been postulated to shed alternating vortices causing pitching/oscillations of the canopy. The results presented provide some insight into which geometric features affect vortex shedding and may enable the redesign of the baseline parachute to minimize instabilities. [Preview Abstract] |
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1B.00032: GEOPHYSICAL |
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1B.00033: An experimental analog for the study of waving marine grass in tidal currents Julia Lee, Ravi Singh, Shreyas Mandre Tidal currents passing through submerged vegetation mix the fluid and facilitate various environmental and ecological transport processes. This fluid-vegetation interaction, where the submerged grasses behave like those on the ground waving from wind, results from a shear instability of the surrounding flow. We devise a two-dimensional lab scale analog of the fluid-vegetation interaction using ABS plastic filaments immersed in a soap film to simulate the grass blades in a tidal flow. The array of filaments spontaneously waves in response to the flow of the soap film. Our experimental system makes direct flow measurement possible for a detailed comparison with theory. [Preview Abstract] |
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1B.00034: GRANULAR FLOWS |
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1B.00035: Measurement of self diffusion in a two-dimensional complex plasma T.E. Sheridan Complex (dusty) plasma is an open, weakly-damped system of charged, microscopic particles which interact through a long-range screened Coulomb force. We have experimentally characterized diffusion in a two-dimensional (2d) liquid complex plasma. The 2d complex plasma is heated naturally by a surrounding three-dimensional toroidal dusty plasma gas. The measured dust velocity distribution functions are isotropic Maxwellians, giving a well-defined kinetic temperature $T$. The mean-square displacement is found to increase linearly with time, indicating normal diffusion. Measured diffusion coefficients increase approximately linearly with $T$. The effective collision rate is dominated by dust-dust collisions rather than neutral gas drag. [Preview Abstract] |
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1B.00036: Contact Dynamics Models for Spacecraft-Regolith Interactions Christine Hartzell, Melany Hunt Granular mechanics simulations are currently used in the planetary science community in order to understand the evolution of asteroids, which are believed to be self-gravitating conglomerates of boulders and smaller grains. These simulations are typically done with Hard-Sphere or Soft-Sphere Discrete Element Method (DEM) codes. However, asteroids are increasingly being considered as exploration targets for the future spacecraft. Due to the very low gravity on the surface of these bodies (in some cases, six orders of magnitude less than Earth's gravity), it is not reasonable to design sample collection devices or mobility systems for future spacecraft based solely on Earth-based experimentation. However, there are limitations to using DEM codes for dense granular systems. Thus, we are creating a Contact Dynamics model to aid in the design of future spacecraft. In addition to its necessity for the design of spacecraft for asteroid exploration, granular mechanics simulations will also reduce the cost and risk of designing future mobility and sample collection systems for spacecraft heading to the Moon and Mars. We will present the current status of our Contact Dynamics code for monodisperse, spherical grains. [Preview Abstract] |
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1B.00037: INDUSTRIAL APPLICATIONS |
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1B.00038: Electric-Field-Enhanced Jumping-Droplet Condensation Nenad Miljkovic, Daniel Preston, Ryan Enright, Alexander Limia, Evelyn Wang When condensed droplets coalesce on a superhydrophobic surface, the resulting droplet can jump due to the conversion of surface energy into kinetic energy. This frequent out-of-plane droplet jumping has the potential to enhance condensation heat and mass transfer. In this work, we demonstrated that these jumping droplets accumulate positive charge that can be used to further increase condensation heat transfer via electric fields. We studied droplet jumping dynamics on silanized nanostructured copper oxide surfaces. By characterizing the droplet trajectories under various applied external electric fields (0 -- 50 V/cm), we show that condensation on superhydrophobic surfaces results in a buildup of negative surface charge (OH-) due to dissociated water ion adsorption on the superhydrophobic coating. Consequently, the opposite charge (H3O$+)$ accumulates on the coalesced jumping droplet. Using this knowledge, we demonstrate electric-field-enhanced jumping droplet condensation whereby an external electric field opposes the droplet vapor flow entrainment towards the condensing surface to increase the droplet removal rate and overall surface heat transfer by 100{\%} when compared to state-of-the-art dropwise condensing surfaces. This work not only shows significant condensation heat transfer enhancement through the passive charging of condensed droplets, but promises a low cost approach to increase efficiency for applications such as atmospheric water harvesting and dehumidification. [Preview Abstract] |
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1B.00039: INSTABILITY |
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1B.00040: Theoretical models for the stability of a liquid ring on a substrate Javier A. Diez, Alejandro G. Gonz\'alez, Lou Kondic A viscous incompressible fluid ring on a partially wetting substrate is studied within the framework of long-wave theory. We found that static equilibria are posible in the presence of contact angle hysteresis. Their linear stability is carried out by using a slip model. A quasi-static approximation is also implemented to analyze longer times. This latter approach takes into account the concomitant variation of the instantaneous growth rates of the modes responsible for either collapse of the ring into a single central drop or breakup into a number of droplets along the ring circumforence. We compare the results of these models with those obtained from nonlinear numerical simulations based on a complementary disjoining pressure model. We find remarkably good agreement regarding the expected number of drops forming during the breakup process. (J. Fluid Mech. {\bf 718}, 246 (2013)) [Preview Abstract] |
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1B.00041: MICROFLUIDS |
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1B.00042: Response of microfluidic fuel cells to secondary flows Massimiliano Rossi, Christian J. K\"ahler Microfluidic or membraneless fuel cells (MFCs) are a recent class of miniaturized fuel cells (Ferrigno et al. 2002, Choban et al. 2004) composed by a microchannel in which a parallel laminar stream of two fluids, a fuel and an oxidant, is established. The fuel and oxidant remain in contact but do not mix due to the absence of turbulence. The simple architecture and the fact that no expensive proton exchange membranes are needed make this configuration technologically very attractive, however the efficiency especially in terms of fuel utilization is still too low to be competitive for practical applications. One limitation is given by the formation of depletion boundary layers at the electrodes that worsen the red-ox reactions. A way to reduce this problem is to use transversal secondary flows to stir the fluid streams and replenish the depletion layers. In this study, we intend to characterize the performance of MFC with curved channels in which the transversal secondary flows are present in the form of two counter-rotating vortices known as Dean vortices. The characterization will be completed by simultaneous measurements of the current intensity and of the flow velocity performed with 3D Astigmatic Particle Tracking Velocimetry. [Preview Abstract] |
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1B.00043: Molecular dynamics simulation of dewetting of ultra-thin liquid film with artificial dry patches Susumu Kono, Ichiro Ueno Large scale molecular dynamics simulations of dewetting of ultra-thin liquid films on a solid substrate are carried out. In case of thin film of nanometer-scale thickness, the liquid film is ruptured spontaneously which is called spinodal decomposition. The instability generates the dry patches in the film. The dewetting process begins from the several dry patches. Finally, the liquid film varies to droplets on the substrate. In the present study, we focus on the dry patch distribution in the liquid film, and investigate the depending of the initial distribution of the dry patches on the final stage of the nanometer-scale droplet formation. First, the liquid film composed by LJ fluids covered solid substrate with the preset dry patches. Then the dewetting behavior based on the artificial dry patches distribution is observed. As a result, it is found that there exists a sharp threshold of the initial radius of the artificial patch to realize the spontaneous rupture. This threshold depends on the initial film thickness, contact line curvature and LJ liquid-solid parameter. In comparing with usual dry patches distribution due to spinodal decomposition to artificial one, the final droplets formation also depends on initial dry patches distribution. [Preview Abstract] |
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1B.00044: Local fluorescence in micro channels for particle counting Mariana Centeno Sierra, Mathieu Hautefeuille, Catalina Stern We produce local fluorescence in polydimethylxiloxane (PDMS) microchannels with a low power laser. This technique can be used to count either particles or cells in microflows. A CCD webcam is mounted on the objective of a microscope to visualize the flow. Particles obstruct the fluorescence as they pass by, allowing for a simple counting method that is software controlled. We present the experimental setup and preliminary results. [Preview Abstract] |
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1B.00045: Study on fabrication of scaffold using three-dimensional electrohydrodynamic ink-jet technique Han Seo Ko, Soo-Hong Lee, Pil-Ho Lee, Dae-Hoon Kim, Chiang Wei Yu, Sang Won Lee The EHD ink-jet technique uses the electrostatic force by applied voltage between a nozzle and an electrode to fabricate a three-dimensional scaffold by accumulating layers. In this study, a PLA (Polylactide) which is a polymer material was used to make the biodegradable scaffold. The experiment was performed by various inks with different solvent ratios because the layer thickness and width on the substrate are influenced by the ink properties such as the solvent ratio and boiling point. The cone-jet mode which looks cone-shaped on the meniscus was used for the EHD jetting by various stage velocities and solvent ratios of the PCL material. The micro-zoom lens and the LED lamp were used to visualize the jetting performance. The three-dimensional printing was completed by the movement of the stages using the Gentry structure. The optimum condition was selected for the fabrication of the scaffold after investigating the width of the pattern and the thickness of the multiple layers. [Preview Abstract] |
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1B.00046: Effect of Inhomogeneous Flow on Micro-scale Biomedical Gas S. Sen In this work the effect of a radially varying parallel equilibrium flow on the stability of the Rayleigh-Taylor mode is studied in a micro-scale confined gas in a biomedical system. It is shown that the parallel flow curvature can completely stabilize the mode. The flow curvature also has a robust effect on the radial structure of the mode. Possible implications of these findings are also discussed. [Preview Abstract] |
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1B.00047: MULTIPHASE FLOWS |
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1B.00048: Energy and Momentum Transport in Microfluidic with Shear-driven Flows S. Sen Transport of the pressure-driven perturbations with a sharp parallel velocity shear is studied in a microfluidic. Studies show when the second derivative of the parallel velocity with respect to the radial coordinate is positive, the linear mode may become unstable and turbulent momentum transport increases. On the other hand, when the second derivative of the parallel velocity is negative, the linear mode is completely stabilised and turbulent momentum transport reduces. Possible implications of this results in biomedical industry will be discussed. [Preview Abstract] |
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1B.00049: NANOFLUIDS . [Preview Abstract] |
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1B.00050: Using instability of nanometric liquid Cu films on SiO2 substrates to determine the underlying van der Waals potential Alejandro G. Gonz\'alez, Javier A. Diez, Yueying Wu, Jason D. Fowlkes, Philip D. Rack, Lou Kondic We study the instability of nanometric Cu thin films on a SiO2 substrate. The metal is melted by means of laser pulses for some tens of nanoseconds. The free surface destabilizes during the liquid lifetime, leading to the formation of holes at first and to metal drops on the substrate in later stages. By analyzing the Fourier transforms of the SEM images obtained during the metal film evolution, we determine the emerging length scales for both early and late stages of the instability development. The results are analyzed within the framework of a long-wave hydrodynamic model, which introduces van der Waals forces by means of disjoining and conjoining pressures. These forces are characterized by a pair of exponents for the ratio $h/h{\ast}$, where $h$ is the liquid thickness and $h_{\ast}$ is a residual one. We find that the pair $(3,2)$ provides a good agreement for the relationship of the wavelength with maximum growth rate, $\lambda_m$, while other typical pairs, such as $(4,3)$ and $(9,3)$ do not provide accurate description of the experimental data (Langmuir {\bf 29}, 9378 (2013)). [Preview Abstract] |
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1B.00051: Lithography-free nanofluidic concentrator based on droplets-on-demand system Miao Yu, Hongbo Zhou, Shuhuai Yao Biomarkers are usually low-abundance proteins in biofluids and below detection limit of conventional biosensors. Nanofluidic concentration devices allow efficient biomolecules trapping by utilizing ion concentration polarization near nanochannels. However, once the electric field is turned off, the electrokinetic concentration plug cannot maintain its concentration status and starts to diffuse. In order to maintain the high concentration and extract the concentrated sample for further analysis, a good approach is to encapsulate these plugs into water-in-oil droplets. Here we developed a nanofluidic concentrator based on droplet-on-demand generator to encapsulate concentrated sample in nL droplets. The lithography-free nanochannels were patterned by thermal cracking on the surface of PS Petri-dish. The resulting nanochannel arrays were 30 nm in depth. In combination with microchannels on PDMS, the micro-nano hybrid chip was developed. We used FITC solution to demonstrate that the chip significantly increased the sample concentration for more than 100 folds within 5 minutes. By tuning the pulsed pressure imposed by the solenoid valve connected to the concentration channel, the system can generate a desired volume of droplet with a target sample concentration at a prescribed time. [Preview Abstract] |
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1B.00052: NON-NEWTOWNIAN FLOWS |
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1B.00053: Toward Generating Low-Friction Nanoengineered Surfaces with Liquid-Vapor Interfaces Chu Wang, Xin Yong, Lucy Zhang Using molecular dynamics (MD), we investigate the importance of liquid-vapor interface topography in designing low friction nanoengineered superhydrophobic surfaces. Shear flow is simulated on patterned surfaces with cylindrical nanoholes and nanopillars. We devise an approach to generate entrapped bubbles with large protrusion angles in MD simulations, where the relationship between the effective slip length and bubble meniscus curvature is attained. We show that protruded bubbles can induce significant friction which hinders the slip characteristics produced on liquid-vapor interfaces. We also demonstrate that the continuity of the liquid-vapor interface greatly influence slip. Good quantitative agreements with previous simulations and analytical models on the asymptotic behavior of slip length with varying gas fraction are obtained. Our results show that we can adopt ideas from continuum scale analysis to design nanoengineered surfaces with large slip, with the caution of detailed interface dynamics at nanoscale. [Preview Abstract] |
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1B.00054: Parameter effects on shear stress of Johnson--Segalman fluid in Poiseuille flows Xiang Qiu, Jianping Luo, Yulu Liu Exact solutions of shear stress versus velocity gradient and the numerical solutions of streamwise velocity distribution in radial direction of a JohnsonSegalman fluid in a circular pipe are obtained. The effects of material parameters, Weissenberg number, ratio of viscosities and slip parameter, on shear stress and streamwise velocity have been considered to investigate the discontinuous velocity derivatives and stick-slip phenomenon at the wall. We find that there is a non-monotonic relationship between the shear stress and rate of shear for certain values of the material parameters and consequently, the velocity profile has discontinuous derivatives. Moreover, the variational range of material parameters is given for the appearance of a non-monotonic relationship between the shear stress and the rate of shear. Finally, we have shown the exact expression of critical pressure gradient and also have given the conditions where spurt phenomena occur. [Preview Abstract] |
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1B.00055: ABSTRACT WITHDRAWN |
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1B.00056: PARTICLE-LADEN FLOWS |
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1B.00057: Pressure Driven Flow of Inhomogeneous Suspensions: Experiments and Theory Ashwin Vaidya, Mehrdad Massoudi, Siobhan Soltau, Gin Sanchez, Jillian Varner, Joseph Fiordilino This study is devoted to the experimental and theoretical investigation of the pipeline flow of low volume fraction suspensions. We derive our motivation from questions concerning the feasibility of pipeline transport of biomass. Our experimental observations, based on a table-top scale study indicate an unusual relationship between flow rate and pressure gradient which has not been observed in homogeneous systems. For our system, which consists of (2{\%}-6{\%} volume fraction) mixtures of mulch/coffee powder/crushed leaves in water, we find that for a certain range of pressure gradients, the flow rate in fact decays for increasing pressures. Based on a generalization of the Newtonian fluid model, we mathematically model our mixture by taking the system's bulk viscosity and being dependent upon the pressure gradient. The resulting expression for flow rate is fitted to experimental data showing a very good correlation. The results of this study provide the only example of a system where a pressure dependent viscosity is valid at low pressures. We also consider a single phase non-Newtonian model for this system where the effects of shear rate and normal stresses are incorporated. [Preview Abstract] |
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1B.00058: Study of Local Profiles Relative to the Particle Surface in a Forced Particle-Laden Turbulent Flow Oscar Castro, Orlando Ayala, Lian-Ping Wang Turbulent flows laden with solid particles, liquid droplets, or air bubbles are relevant to many engineering applications and biological and environmental processes. When the particle size is much smaller than the Kolmogorov scale of the carrier flow, the motion of the particle can be described by a point-particle model. Currently, it is not clear how to treat the interaction of a solid particle with the carrier flow when its size is comparable or larger than the Kolmogorov scale. Here we address the interaction of finite-size particles with the carrier fluid turbulence using lattice-Boltzmann-based, particle-resolving simulations. Our recent results (Comput. \& Math. with Applications, DOI: 10.1016/j.camwa.2013.04.001) on forced turbulence laden with non-sedimenting solid particles at a particle-to-fluid density ratio of 5, solid volume fraction of 0.102, and particle diameter to Kolmogorov length ratio of 8.05 reveal that the enhanced viscous dissipation is related to the local flow profiles near the particle surface. Here we repeat this simulation and present more accurate local profiles by averaging over time in addition to space. We will also analyze how such profiles change with the particle volume concentration and the particle size relative to the Kolmogorov scales. [Preview Abstract] |
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1B.00059: Two-way Interactions in Particle-Laden Turbulent Channel Flow Cheng Peng, Oscar Castro, Orlando Ayala, Lian-Ping Wang Most previous studies of two-way interactions in particle-laden turbulent channel flows were performed using the point-particle approach. Here we present preliminary results on two-way coupling of finite-size particles with turbulence in a channel flow. The lattice Boltzmann approach is used to resolve both the channel flow and the disturbance flows around moving particles. Results of single-phase turbulent channel flows are first compared to published benchmark DNS results to validate the lattice Boltzmann approach. Preliminary results on turbulent particle-laden channel flow are analyzed at three levels: whole-field, phase-partitioned, and profiles as a function of distance from the surface of solid particles. We will examine the effects of finite particle size on the mechanisms of energy production and dissipation. Specifically, the two-way interactions near the channel wall are contrasted with those away from the walls. Results will be compared to those based on the point particle approach. We will also study how the results change with particle size, particle-to-fluid density ratio, and particle volume fraction. [Preview Abstract] |
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1B.00060: Computationally and experimentally assessed gravity-driven, mono- and bidisperse, particle-laden flows Shreyas Kumar, Kaiwen Huang, Matt Hin, Gilberto Urdaneta, Aliki Mavromoustaki, Jeffrey Wong, Sungyon Lee, Andrea Bertozzi We present an experimental study which investigates the motion of granular materials in mono- and bi-disperse suspensions consisting of silicone oil, glass and ceramic beads. The beads are of distinct densities both denser than the oil but of approximately the same size. A finite volume of slurry is allowed to flow down an inclined plane and the subsequent flow development is recorded. The system parameters are the angle of inclination, the total particle concentration and the relative amount of heavy (ceramic) to light (glass) beads. Similarly to the results observed in previous studies of mono-disperse slurry flows, in bidisperse suspensions, there exist two stable flow regimes: the first one involves settling of particles to the substrate while, in the second one, the particles aggregate at the front of the flow. We carry out a series of experiments to investigate the effect of system parameters on the resulting flow regime patterns and compare our results with a theoretical model which incorporates the effects of shear-induced migration and sedimentation in bidisperse suspensions of negatively buoyant particles. Further, we use fluorescent particle beads to compare the particle spatio-temporal evolution observed in experiments against numerical simulations. [Preview Abstract] |
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1B.00061: ABSTRACT WITHDRAWN |
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1B.00062: POROUS MEDIA FLOWS |
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1B.00063: ABSTRACT WITHDRAWN |
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1B.00064: ROTATING FLOWS |
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1B.00065: The interfacial dynamics between two immiscible rotating fluids Hua-Yi (Maggie) Hsu We numerically investigated the topological interface change occurring between two rotating, immiscible, stratified fluids. We simulate the two- layer fluid in a cylindrical container which is driven by a disk with a constant angular velocity. The upper fluid is of higher viscosity than the lower one, and the ratio of the radius of cylindrical container and the depth of the upper fluid is set to be one of the parameters. The surface tension between 2 fluids is one of the key control factors which change the topological interface. The interface behaviors were found over a wide range of parameters. The topological interface shape will be found such as: hill, plateau, bell, drop formation, and chaos. We also investigate the size of drop using different parameters. [Preview Abstract] |
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1B.00066: SUSPENSIONS |
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1B.00067: Liquid flow between hydrodynamicaly interacting particles in confined systems Alvaro Gomez Marin, Massimiliano Rossi, Christian J. Kaehler Particle suspensions in confined geometries are greatly complex systems since they introduce a high degree of complexity into the otherwise linear Stokes flows. Very recently, new mechanisms of instability have been identified in simulations in confined shear-flows of non-Brownian dilute particle solutions (Zurita-Gotor et al., J. Fluid Mech. 592, 2007, and Phys. Rev. Lett. 108, 2012). In this study we will focused on particle pairs interacting with walls, which requires the use of micro-confined systems. By the use of Astigmatism-PTV on particle solutions with different fluorescent characteristics, we will solve both the non-Brownian interacting particle trajectories and the flow around them in order to elucidate the details of the hydrodynamic particle-particle interactions. [Preview Abstract] |
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1B.00068: Measurements of wall shear stress in a planar turbulent Couette flow with porous walls Paul Beuther Measurements of drag on a moving web in a multi-span festoon show a stronger than expected dependency on the porosity of the web. The experiments suggest a wall shear stress 3-4 times larger than non-porous webs or historical Couette flow data for solid walls. Previous DNS studies by Jimenez et.al. (JFM Vol 442) of boundary layers with passive porous surfaces predict a much smaller increase in wall shear stress for a porous wall of only 40{\%}. Other DNS studies by Quadrio et.al. (JFM Vol 576) of porous walls with periodic transpiration do show a large increase in drag under certain periodic conditions of modest amplitude. Although those results are aligned in magnitude with this study, the exact reason for the observed high drag for porous webs in this present study is not understood because there was no external disturbance applied to the web. It can be hypothesized that natural flutter of the web results in a similar mechanism shown in the periodic DNS study, but when the natural flutter was reduced by increasing web tension, there was only a small decrease of the drag. A key difference in this study is that because of the multiple parallel spans in a festoon, any transpiration in one layer must act in the opposite manner on the adjacent span. [Preview Abstract] |
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1B.00069: Atmosphere-ocean exchanges over slow and fast wave fields Qi Li, Elie Bou-Zeid, Nikki Vercauteren, Marc Parlange We explore the influence of surface gravity waves on momentum and scalar exchanges between the atmosphere and underlying water surfaces, based on field experimental data sets. The existence of both slow (occurring under active local wind forcing) and fast (swell) waves and their interactions with the atmosphere show unique features compared to flow over fixed walls. While turbulence and fluxes over slow waves surfaces share many features with flow over fixed surfaces, fast moving waves complicate the picture with different ranges of scales transporting momentum in opposite vertical directions. We further show that, especially under fast-wave conditions, the surface waves' phase velocity and directionality influence the form drag at the surface, inducing a misalignment between the surface stress and wind velocity vectors. This improved understanding allows us to re-approach how classic loglaws and their extension to non-neutral conditions (the Monin-Obukhov similarity theory) are formulated and applied over the marine/water surface. Particularly, we show that the appropriate air velocity parameter to use in these laws is the difference between the wind velocity component parallel to the wave propagation direction and the wave phase velocity. [Preview Abstract] |
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1B.00070: Comparison between Prandtl, Navier-Stokes and Euler solutions for 2D flows in the presence of solid boundaries Marie Farge, Romain Nguyen van yen, Matthias Waidmann, Kai Schneider, Rupert Klein In 1904 Prandtl introduced the notion of boundary layer (BL), assuming all viscous energy dissipation takes place only in the BL (as long as it remains in contact with the body) whose thickness is inversely proportional to the Reynolds number, $Re$. He derived the BL equation and succeeded to asymptotically match its solution with that of an inviscid fluid flow governed by Euler's equation outside the BL. In the poster we address the following question: does energy dissipate when the BL detaches from the solid body? We consider a jet, modeled as a vorticity dipole, impinging onto a wall, that we study by Direct Numerical Simulation to see how solutions behave in the vanishing viscosity limit (equivalent to the limit of large $Re$). Starting from the same initial flow and the same geometry, we compare the solutions obtained for Euler's equation, Prandtl's equation, and Navier-Stokes equation, using different numerical methods. We observe that in the vanishing viscosity limit energy dissipation does not tend to zero, in a BL whose thickness scales as $Re^{-1/2}$ (as predicted by Prandtl's 1904 theory), but produces vortices at the wall which entrain the BL and roll it up to form a dissipative structure, whose thickness scales as $Re^{-1}$ (Kato, 1984), which detaches from the wall. [Preview Abstract] |
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1B.00071: Non-Dimensionalization and Scaling of Helmholtz Equation and Schrodinger Equation, Which Reformulated for Fluid Dynamics Ahmad Reza Estakhr In fluid mechanics, the Reynolds number (Re) is a dimensionless number $R_e=\frac{F_int}{F_vis}$ I defined Reynolds number in a different situation, through the Helmholtz equation which represents the time-independent wave equation, $\nabla^2\psi+k^2\psi=0$ Now i consider wave vector $k$ as Reynolds number per a characteristic linear dimension so, $\nabla^2\psi+\frac{R_e^2}{L^2}\psi=0$ which led to the non-dimensionalization and scaling of Helmholtz equation, $L^2\nabla^2\psi+R_e^2\psi=0$ this equation is applicable to fluid dynamics. then I reformulate schrodinger equation, $-\frac{\mu^2}{2\rho}\nabla^2\psi +U_v\psi=E_v\psi$ where the $\mu$ denotes viscosity, $\rho$ is density, $U_v$ and $E_v$ are potential and total energy per unit volume. non-dimensionalization tricks: $\frac{\mu^2}{2\rho}=\frac{\mu Lv}{2R_e}$ where the $v$ is velocity, $L$ is linear dimension. now if we take factor of $\frac {\mu v}{L}$ from both side of equation, the Non-dimensionalization and scaling of schrodinger equation for fluid dynamics will be, $-\frac {L^2}{2R_e}\nabla^2\psi +U_v^*\psi=E_v^*\psi$ [Preview Abstract] |
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1B.00072: Kinetic Energy-Preserving Discretization Schemes for High Reynolds Number Propulsive Applications Ayaboe Edoh, Ann Karagozian The overarching goal of this project is to explore numerical approaches for the study of turbulent flows and to use them to explore the fundamental physics of combustion processes relevant to airbreathing and rocket propulsion systems. The present studies involve an investigation of kinetic energy-preserving discretization schemes that enable multiple ways for tracking acoustic versus particle waves in a compressible flowfield. Semi-discretized schemes have been explored, with a comparison of collocated and staggered grids and alternative multi-stage ODE schemes for time integration. The energy behavior of Crank-Nicolson collocated schemes is similarly explored, for example, for the scalar, inviscid Burger's equation and for the 1D compressible Euler equations. Comparisons of accuracy for different order codes with different dissipation coefficients and using different types of boundary conditions are made, including schemes that demonstrate the lack of requirement for artificial dissipation and strong energy preservation. [Preview Abstract] |
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1B.00073: VORTEX DYNAMICS |
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1B.00074: The Moore Singularity in the Evolution of a Vortex Sheet through Longitudinal Diffusion Ujjayan Paul The phenomenon of singularity in vortex sheets starting from analytic initial data has been studied in detail by various authors. Standard numerical solution of the vortex sheet using line vortex approximation indicates a singularity at a finite critical time.However, the possibility of a weak solution to the vortex sheet problem at all time has been raised before.The weak solution is based on the convergence of the vortex blob method in the limit of zero blob size. Regularization techniques have been applied on point vortex models. In a real fluid the problem of finite time singularity is eliminated by viscosity. Here we shall discuss and compare two possible regularization techniques applied on a vortex sheet model, which allows us to continue the evolution much beyond the critical time as predicted by Moore. [Preview Abstract] |
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1B.00075: POST-DEADLINE |
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1B.00076: Interfacial waves generated by contact line motion through electrowetting Jonghyun Ha, Jaebum Park, Yunhee Kim, Jungmok Bae, Ho-Young Kim The contact angle of a liquid-fluid interface can be effectively modulated by EWOD (electrowetting on dielectric). Rapid movement of the contact line, which can be achieved by swift change of voltages at the electrodes, can give rise to interfacial waves under the strong influence of surface tension. Many optofluidic devices employing EWOD actuation, such as lenses, three-dimensional displays and laser radar, use two different liquids in a single cell, implying that the motions of the two liquids should be considered simultaneously to solve the dynamics of interfacial waves. Furthermore, the capillary waves excited by moving contact lines, which inherently involve slipping flows at solid boundaries, pose an interesting problem that has not been treated so far. We perform a perturbation analysis for this novel wave system to find the dispersion relation that relates the wavenumber, and the decay length over which the wave is dissipated by viscous effects. We experimentally corroborate our theory. [Preview Abstract] |
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1B.00077: Eigenmode analysis of advective-diffusive transport in micromixers by the diffusive mapping method Patrick Anderson, Michel Speetjens, Oleksandr Gorodetskyi, Max Giona Advective-diffusive transport in microflows is studied by means of the diffusive map- ping method, a recent extension of the mapping method by Gorodetskyi et al. (Phys. Fluids 24, 2012) that includes molecular diffusion. This greatly expands the application area of the mapping technique and makes the powerful concepts of eigenmode decompo- sition and spectral analysis of scalar transport accessible to an important class of flows: inline micromixers with diffusion. The staggered herringbone micro-mixer is adopted as a prototypical three-dimensional micro mixer. Simulations with the diffusive mapping method are in close agreement with experimental observations in literature and expose a strong impact of diffusion on the transport. Diffusion enables crossing of Lagrangian trans- port barriers and thus smoothens concentration gradients and accelerates homogenization. Spectral analysis of the mapping matrix reveals this already occurs on a modal level in that individual eigenmodes progressively smoothen and spread out across transport bar- riers with stronger diffusion. Concurrently, the corresponding eigenvalues diminish and thus fundamentally alter the mixing process by invariably causing homogenization, irre- spective of the Lagrangian flow structure. This happens faster and exhibits an earlier emergence of the dominant eigenmode the stronger the diffusion. Lagrangian structures may still affect the spectral properties in that flows comprising both islands and chaotic seas typically result in a richer set of eigenmodes compared to cases with global chaos. [Preview Abstract] |
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1B.00078: A combined RANS-LES simulation of a turbulent round jet in a large enclosure Sasan Salkhordeh, Sagnik Mazumdar, D. Tyler Landfried, Anirban Jana, Mark Kimber A combined RANS-LES simulation of a round turbulent jet confined in a large cylindrical enclosure is conducted. As the computational cost of doing LES over the entirety of the large enclosure is high, LES is done only near the jet axis. First, steady, axisymmetric RANS simulation of the confined jet is performed using a thin wedge-shaped slice of the enclosure. The RANS results are validated with experimental data from literature. LES is then performed in a small cylindrical domain around the jet, with initial and boundary conditions provided by the validated RANS results. After comparing six Sub-Filter Stress (SFS) models, the SFS model chosen for the LES simulation is a variant of the dynamic Smagorinsky model. The effect of inlet flow profile and turbulent fluctuations on the evolution of the jet is investigated. The influence of filter characteristics on simulation results is also analyzed. Finally, the LES results are compared with experimental measurements. [Preview Abstract] |
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1B.00079: Dynamic behavior of electrowetting-based liquid prisms Jaebum Park, Jonghyun Ha, Kyuhwan Choi, Jungmok Bae, Ho-Young Kim A liquid prism is an optofluidic device consisting of two immiscible liquids, whose interface acts as a refractive surface. To steer a light beam that constructs optical images, the interface profile, or the contact angle, is modulated via electrowetting on dielectric (EWOD). Alternating current (AC) voltages are used for liquid prisms to stably maintain a desired contact angle without charge saturation in general. However, minute oscillations at the contact line are observed due to rapid changes of voltages under AC conditions, which may propagate into the interface leading to the deterioration of the optical quality. Here we find that the oscillation behavior is strongly correlated with the type of electrolytes, so that the solutions of small ions are more vulnerable to oscillations. We give an empirical relationship of the oscillation amplitude to the AC frequency, and theoretically analyze the salient features of the electrowetting-driven interface motion. [Preview Abstract] |
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1B.00080: Space-Time Pressure-Velocity correlations in a high Reynolds number Turbulent boundary Layer Yoshitsugu Naka, Michel Stanislas, Jean Marc Foucaut, S\'ebastien Coudert In the present study, we developed an experimental setup for the simultaneous measurements of the fluctuating pressure and the three velocity components in a high Reynolds number turbulent boundary layer. A quantitative measure of the extension of the space-time pressure-velocity correlations is given based on their reconstructed 3D distributions. The correlations between the fluctuating pressure at the wall and in the field and each three velocity components exhibit characteristic behavior. The pu correlation show significant Reynolds number dependence which is less evident for the two other correlations. The wall pressure velocity correlation are significantly different from the field ones. All correlations evidence strong relation of the pressure fluctuations with large scale coherent structures. These relations are significantly different for positive and negative pressure fluctuations at the wall. [Preview Abstract] |
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1B.00081: Shear Driven-Streaming Potential Flow in a Charged Slit Microchannel Behnam Khorshidi, Subir Bhattacharjee The flow behavior in microfluidic devices is of great importance due to the need of precise control of the mass and momentum transport in these small scale channels. In the case of two-phase flow, e.g. the stratified flow of an oil layer above an aqueous phase, the situation becomes more interesting, but complicated. In most cases, the interface between the liquids is electrically charged due to the presence of the dissolved ions or colloidal particles. Therefore, there is a possibility that the physicochemical properties of the interface affect the flow behavior. The objective of the present study is to develop a fundamental understanding of flowing oil-water interface, with particular focus on the role of electrical forces acting at this layer. Analytical expressions are derived to describe the electrokinetic effects of electric double layer (EDL) on the shear-driven flow of an aqueous electrolyte solution between a moving and a stationary wall, the moving wall representing the charged oil-water interface. The flow field is obtained under a wide range of operating conditions. The results show that the velocity profile changes significantly depending on the surface potential of the moving wall, which reveals the importance of convective transport of ions near the mobile interface. [Preview Abstract] |
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1B.00082: Experimental investigation and analysis of continuous flow through trace gas preconcentrator Jihyun Kim It was proposed by Muntz et al. in 2004 to study a micro/mesoscale continuous flow through trace gas preconcentrator, which could avoid the time fidelity problem. The preconcentrator for rarefied trace gas analysis, which is one part of a gas detector or analyzer, has been built and consists of a main flow channel, pumping chambers, and separation membranes that are located upper and lower surface of the main flow channel. The preconcentration is not from stop, adsorption, and release, but is caused by the gradually decreasing cross section of the main flow channel until release through the detection unit such as gas chromatography, mass spectrometry, or optical diagnostics. This has the possibility of achieving concentration increase of various gases in a carrier gas by using relatively simple micro/macroscale mass diffusion separation stages, and is suitable for improving the time accuracy of analytical systems. A series of experiments were conducted in an attempt to validate the available numerical data, such as the concentration and gas flow speed of the newly continuous preconcentration technology. This study involved experimental investigations to obtain a base-line comparison of the existing numerical predictions provided by the prototype preconcentrator. [Preview Abstract] |
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1B.00083: Theoretical models for trace gas preconcentrators Jihyun Kim Muntz et al., in 2004 and 2011, had attempted to describe theoretical models about the shape of a main flow channel and the concentration ratio of trace gas for a Continuous Flow-Through Trace Gas Preconcentrator by concepts of net flux and mass flow rate respectively. The possibilities were suggested to obtain theoretical models for the preconcentrator even through they were not satisfied with experimental results, because the theoretical models were only considered for free molecular flow. In this study, new theoretical models based on net flux and mass flow rate have been applied for each regime; free molecular flow, transition flow, and hydrodynamic flow. There are comprehensive numerical models to describe entire regimes with the new theoretical models induced by mass flow rate, but the new theoretical models induced by net flux can be only obtained for the hydrodynamic flow. The numerical predictions were compared with existing experimental results of the prototype of the preconcentrator. The numerical predictions of hydrodynamic and transition flows by mass flow rate were close to the experimental results, but other cases were different to the experimental data. Nevertheless, the theoretical models can provide the possibility to develop the theory of preconcentrator. [Preview Abstract] |
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1B.00084: Energy-Efficient Rate-Based Particle Separation Diana Lievano, Tathagata Bhattacharya, Joseph McCarthy The effective separation of particles is key to numerous processes and industries handling solid materials. Despite this fact, particle separations techniques remain typically quite ``low tech'' and often are energy-intensive (e.g., sieving) or environmentally unfriendly (e.g., froth floatation) or both. Rate-based separation processes, on the other hand, represent a unique approach to particle separation that has the potential to be more flexible, more efficient, and more environmentally friendly than existing ``low tech'' techniques. In the present paper, we highlight passive granular ratchets, where particles of differing properties flow through a device often called a Galton board. In this type of device, the gravity-driven flow of particles down an inclined plane causes collisions between the particles and the evenly distributed pegs along the board. Dissipative collisions between particles as well as between paticles and pegs results in a diffusion-like motion of particles perpendicular to the flow. The extent of separation (i.e., how far one type of particle is removed from another) depends on the different distances traversed by the two types of particles and, ultimately, on the collision rate and energy dissipation for particle-peg events. A simple theory, will be set. [Preview Abstract] |
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1B.00085: 3D CFD Simulation of Horizontal Spin Casting of High Speed Steel Roll Konstantin Redkin, Boris Balakin, Christopher Hrizo, Jeffrey Vipperman, Isaac Garcia The present paper reports some preliminary results on the multiphase modeling of the melt behavior in the horizontal spinning chamber. Three-dimensional (3D) computational fluid dynamics (CFD) model of the high speed steel (HSS) melt was developed in a novel way on the base of volume-of-fluid technique. Preliminary 3D CFD of the horizontal centrifugal casting process showed that local turbulences can take place depending on the geometrical features of the ``feeding'' arm (inlet), its position relative to the chamber, pouring rates and temperatures. The distribution of the melt inside the mold is directly related to the melt properties (viscosity and diffusivity), which depend on the temperature and alloy composition. The predicted liquid properties, used in the modeling, are based on actual chemical composition analysis performed on different heats. [Preview Abstract] |
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1B.00086: The effect of stress-free shapes on the red blood cell dynamics Prosenjit Bagchi, Daniel Cordasco, Alireza Yazdani We present 3D numerical simulations on the effect of the two different stress-free shapes on the dynamics of red blood cells. We observe that in a high viscosity medium, the cell with a nearly-spherical stress-free state undergoes transition from tank-treading to tumbling at a much lower capillary number than the cell with a biconcave stress-free shape. The cell with the biconcave stress-free shape easily loses the biconcave shape and exhibits large time-periodic shape oscillation and membrane folding, while the cell with the nearly-spherical stress-free state retains the biconcave shape without any membrane folding. In a low viscosity medium, however, both stress-free shapes exhibit almost the same dynamics that is characterized by cell tumbling. We then compare the orbital reorientation of the cell for the two stress-free states. In the high viscosity medium, both cells undergo a precession motion orienting their symmetry axis towards the vorticity axis at low capillary numbers, or a kayaking motion orienting the axis towards the shear plane at higher capillary numbers. The capillary number for the precession-to-kayaking transition is observed to be higher for the biconcave stress-free shape than that for the nearly-spherical stress-free shape. At low viscosity medium, both shapes exhibit qualitative similar precession dynamics. [Preview Abstract] |
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1B.00087: Physical Prototype Development for the Real-Time Detection and Mitigation of Hazardous Releases into a Flow System Sara Rimer, Nikolaos Katopodes The threat of accidental or deliberate toxic chemicals released into public spaces is a significant concern to public safety. The real-time detection and mitigation of such hazardous contaminants has the potential to minimize harm and save lives. In this study, we demonstrate the feasibility of feedback control of a hazardous contaminant by means of a laboratory-scale physical prototype integrated with a previously-developed robust predictive control numerical model. The physical prototype is designed to imitate a public space characterized by a long conduit with an ambient flow (e.g. airport terminal). Unidirectional air flows through a 24-foot long duct. The ``contaminant'' plume of propylene glycol smoke is released into the duct. Camera sensors are used to visually measure concentration of the plume. A pneumatic system is utilized to localize the contaminant via air curtains, and draw it out via vacuum nozzles. The control prescribed to the pneumatic system is based on the numerical model. [Preview Abstract] |
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1B.00088: Cooling of a Tapped Granular Column Anthony Rosato, Luo Zuo, Denis Blackmore We present the results of a discrete element investigation of the cooling of a tapped column of uniform, inelastic spherical particles ($d)$ as it evolves to a state of zero kinetic energy. A linear loading-unloading soft contact model is employed, while tapping is simulated by applying a half-sine pulse of amplitude $a$/$d$ and frequency $f$ to a rigid floor supporting the column. For sufficiently energetic taps, the column dilates and then contracts over a time scale $t_{s}$, which depends on the number of particles $N$, restitution coefficient $e$, as well as tap parameters ($a$/$d$, $f)$. Simulation data for (\textit{1} $\le N \le $ \textit{50}) with other parameters being held constant suggested that a time-averaged collision frequency $f_{\mathrm{c}}$ scaled with $N$. Values of $t_{s}$, determined by identifying the instant when the kinetic energy thereafter remained less than \textit{0.001{\%} }of its maximum value, were well-correlated with the form $\alpha (e)N^{-1} + \beta (e)$. Lastly, simulations were in good agreement with physical considerations, suggesting that $t_{s}$ should scale with (1 -- $e^{2})^{-1}$ and inversely with $f_{\mathrm{c}}$. [Preview Abstract] |
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1B.00089: A Dynamical Systems Approach to the Alpha Problem for Rayleigh-Taylor Daniel Israel Turbulent mixing of the unstable Rayleigh-Taylor layer is observed to exhibit self similar growth which scales as $h=\alpha\mbox{At}gt^{2}$. This quadratic growth can be theoretically derived through several different approaches including bubble dynamics, flux balances (Cook et al., 2004), similarity theory (Ristorcelli and Clark, 2004), or simple turbulence modeling. In all these approaches, however, the value of $\alpha$ must be determined empirically. Furthermore, it is not clear from the theory whether $\alpha$ is universal. In fact, reported experimental values for $\alpha$ exhibit a wide variation, almost all of which are well above the values seen in simulations, as documented by Dimonte et al. (2004). That study concluded that all the variation could likely be explained by the presence, or absence, of long wavelength perturbations which can effect the growth for quite a long time. The current work provides a new tool for investigating the transient behavior. Starting with an advanced moment closure model and applying an integral method is shown to result in a set of ordinary differential equations which can be viewed as a low-order model of the turbulence as it evolves towards a self-similar state. Applying the tools of dynamical systems we can examine the possible trajectories of the system in state space. This suggests a new physical picture of how long wavelengths might create the appearance of a high value of $\alpha$. It also gives us a new set of metrics for validating turbulence models for non self-similar problems. [Preview Abstract] |
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1B.00090: Modeling Dilute Gas-Solid Turbulent Flows using Moment Methods Dennis Dunn, Kyle Squires Numerically modeling particle-fluid interactions in turbulent two-phase flows has proven quite useful, and although Lagrangian particle-tracking methods are a plausibly accurate approach, these models are often limited to dilute flows and can be inaccurate in regions of locally large particle concentrations where inter-particle interactions and effects of two-way coupling can be significant. These and other considerations motivate the current effort aimed at implementing Eulerian-based approaches that treat the particle phase as a continuum. The specific focus of the current effort is on modeling dilute particle-laden turbulence in which the gas-phase carrier flow is populated with a second phase of small, dispersed solid particles possessing material densities much larger than that of the carrier flow, and consequently large particle Stokes numbers. The approach adopted in this work is derived from the quadrature-based method of moments. Simulations are conducted of a particle-laden turbulent boundary layer. The gas-phase carrier flow is computed using DNS and the results show that the carrier flow drives the particulate phase via the drag force and with resulting structural interactions, e.g., preferential concentration of particles, similar to those observed in Lagrangian particle tracking simulations. Further comparisons are made against simulations using Lagrangian particle tracking of the dispersed phase and demonstrate the utility of the Eulerian approach, e.g., with statistical descriptors in reasonable agreement between the two methods. [Preview Abstract] |
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1B.00091: The Effects of a Spatially Variant Velocity Field On Stretching: Intuitive Measures Jason Nixon, David Bigio Laminar mixing theory describes the `goodness' of mixing as a function of increased surface area shared between two fluid species. Previous work describes mixing from a post processing perspective, as a function of stretching history, while disregarding the underlying flow. In this work, mathematical measures are derived which predict fluid-fluid interface behavior in a flow and explore the underlying flow field. This family of measures creates an intuitive basis for the exploration interfacial growth. One set of measure relates velocity to the principal directions while the second set relates interfacial orientation with the principal directions. To explore the usefulness of these new measures, they are simulated in three flows; shear flow, divergent flow, and the spatially variant lid driven cavity. In these geometries, the new family of measures proves valuable for demonstrating growth regime characteristics, transitions in growth regime, as well as other flow characteristics unique to each field. It has been shown that the changes in mixing consistent with reorientation occur after a rapid change in the relationship of the flow and principle directions. The second set of measures in this family allows for interface growth and modeled to be studied more objectively. [Preview Abstract] |
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1B.00092: Nature-Inspired Airfoils for Environmental Noise Reduction Suyeong Han, Richard Kyung Recently, study on the insects' flapping flight became one of the challenging research subjects in the field of environmental engineering and aeronautics because of its potential applicability to intelligent micro-robots capable of autonomous flight and the next generation aerial-vehicles. In order to uncover its curious unsteady characteristics, many researchers have conducted experimental and computational studies on the unsteady aerodynamics of insects' flapping flight. In the present work, the unsteady flow physics around insect wings are conducted by utilizing numerical and computational simulation. The e-AIRS [6] (e-Science Aerospace Integrated Research System) gives a balanced service between computational and experimental aerodynamics, along with integrated research process of these two research activities. This paper presents the wing motions and their aerodynamics with a two dimensional approach to reduce environmental noise during the airflight. Also this paper shows an optimal phase angle, where the thrust is maximized at the position of minimized drag, which occurs when noise is minimized. Aside from the two-dimensional approach, stroke angles and phase angles of the airfoils are set as parameters, to determine which motion yields the best aerodynamic characteristics. [Preview Abstract] |
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