Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session F1: Poster Session (6:15 - 7:00 PM) |
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Room: Level 2 Lobby |
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F1.00001: AERODYNAMICS AND ACOUSTICS |
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F1.00002: Vortex shedding by matched asymptotic vortex method Xinjun Guo, Shreyas Mandre An extension of the Kutta condition, using matched asymptotic expansion applied to the Navier-Stokes equations, is presented for flow past a smooth body at high Reynolds number. The goal is to study the influence of unsteady fluid dynamical effects like leading edge vortex, unsteady boundary layer separation, etc. In order to capture accurately the location and strength of vortex shedding, the simplified Navier-Stokes equations in the form of boundary layer approximation are solved in the thin inner region close to the solid body. In the outer region far from the structure, the vortex methods are applied, which significantly reduces the computational cost compared to CFD in the whole domain. With this method, the flow past an airfoil with two degrees of freedom, pitching and heaving, is investigated. [Preview Abstract] |
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F1.00003: A reduced model for vortex shedding from a body using matched asymptotics Shreyas Mandre, Xinjun Guo, Ponnulakshmi V. K. Flow around a solid body at high Reynolds number is often computed efficiently using inviscid vortex methods, if the distribution of vorticity shed from the surface of the body can be predicted accurately. The only method currently available for predicting the shed vorticity is by the application of the Kutta condition, which applies to slender wings at the leading and trailing edges. Therefore, benefit from the high Reynolds number approximation is limited to situations where the Kutta condition is applicable. We present a method based on matched asymptotic analysis to compute the strength and distribution of vorticity shed from rigid bodies of smooth but otherwise arbitrary shape executing arbitrary motion in a uniform far-field flow. The method decomposes he flow domain in an inviscid outer region and a thin viscous boundary layer near the solid body. The flow is approximated by inviscid vorticity dynamics in the outer region and Prandtl's boundary layer theory in the boundary layer. The treatment of the boundary layer dynamics may be considered analogous to the Kutta condition, which yields an approximation to the shed vorticity. An approximately 100-fold increase in computational speed may be achieved using this method compared to direct numerical simulations. [Preview Abstract] |
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F1.00004: Kinematics and Flow Evolution of a Flexible Wing in Stall Flutter John Farnsworth, James Akkala, James Buchholz, Thomas McLaughlin Large amplitude stall flutter limit cycle oscillations were observed on an aspect ratio six finite span NACA0018 flexible wing model at a free stream velocity of 23 m/s and an initial angle of attack of six degrees. The wing motion was characterized by periodic oscillations of predominately a torsional mode at a reduced frequency of k $=$ 0.1. The kinematics were quantified via stereoscopic tracking of the wing surface with high speed camera imaging and direct linear transformation. Simultaneously acquired accelerometer measurements were used to track the wing motion and trigger the collection of two-dimensional particle image velocimetry field measurements to the phase angle of the periodic motion. Aerodynamically, the flutter motion is driven by the development and shedding of a dynamic stall vortex system, the evolution of which is characterized and discussed. [Preview Abstract] |
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F1.00005: Vorticity Transport on a Flexible Wing in Stall Flutter James Akkala, James Buchholz, John Farnsworth, Thomas McLaughlin The circulation budget within dynamic stall vortices was investigated on a flexible NACA 0018 wing model of aspect ratio 6 undergoing stall flutter. The wing had an initial angle of attack of 6 degrees, Reynolds number of $1.5 \times 10^5$ and large-amplitude, primarily torsional, limit cycle oscillations were observed at a reduced frequency of $k= \pi f c / U = 0.1$. Phase-locked stereo PIV measurements were obtained at multiple chordwise planes around the 62.5\% and 75\% spanwise locations to characterize the flow field within thin volumetric regions over the suction surface. Transient surface pressure measurements were used to estimate boundary vorticity flux. Recent analyses on plunging and rotating wings indicates that the magnitude of the pressure-gradient-driven boundary flux of secondary vorticity is a significant fraction of the magnitude of the convective flux from the separated leading-edge shear layer (Wojcik and Buchholz, J. Fluid Mech. 2014; Buchholz et al. AIAA Paper 2014-0071), suggesting that the secondary vorticity plays a significant role in regulating the strength of the primary vortex. This phenomenon is examined in the present case, and the physical mechanisms governing the growth and evolution of the dynamic stall vortices are explored. [Preview Abstract] |
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F1.00006: ABSTRACT WITHDRAWN |
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F1.00007: BIOLOGICAL FLUID DYNAMICS |
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F1.00008: Modeling of Shear-Induced Red Blood Cell Migration for Guiding Microfluidic Device Design Eden Durant, Adam Higgins, Kendra Sharp Through refinement and extension of a two-phase flow model previously reported for modeling blood in cylindrical flows (Gidaspow, 2009), we have developed a computational model for blood flow in complex microfluidic. Treating plasma as a Newtonian fluid and the Red Blood Cells (RBCs) as a granular phase, whose local concentrations are determined statistically, we have captured the migration of RBCs and concomitant formation of a cell free plasma layer at the channel walls. This model provides us with a three-dimensional distribution of RBCs and the development of the stead-state flow profile, and enables us to study the influence of complex microfluidic geometries, including flow obstacles and varying channel dimensions, on the rate and extent of RBC margination. Simulations on 50 and 100 micron square channels match observed trends including decreasing RBC margination rate in larger channels, increasing RBC margination rate with higher hematocrit, and decreasing cell free layer width with increasing hematocrit. This predictive capability will allow microfluidic devices to be tailored and optimized for specific biomedical applications such as separation of blood constituents.. [Preview Abstract] |
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F1.00009: Hydrodynamics of Sessile Choanoflagellates Greg Bustamante, Hoa Nguyen Choanoflagellates are unicellular organisms whose intriguing morphology includes a set of collars/microvilli emanating from the cell body, surrounding the beating flagellum. Certain types of choanoflagellates are sessile, i.e., they can attach themselves to a substrate via a pedicel which extends from the cell body. We investigate the interactions of the flagellum - microvilli - pedicel system in the feeding behavior of sessile choanoflagellates using the method of images for regularized Stokeslets. The results of the fluid-particle motions and streamlines explain their effective capture of bacteria in the fluid. [Preview Abstract] |
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F1.00010: Determining Suction Feeding Efficiency in the Bowfin fish (Amia) using Particle Image Velocimery and Computaional Fluid Dynamics Yenny Rua, Karim Kharbouch, Christopher Sanford, Shanon Reckinger Suction feeding is the most common form of prey capture in aquatic vertebrates. During the early evolution of fishes there was a major change in shape of the mouth, from a wedge shaped mouth opening in more primitive fishes to a more circular and planar mouth. This change in shape resulted from increased mobility of a key upper jaw bone, the maxilla. It has been suggested that this change in shape dramatically increased suction feeding efficiency. This study examines the hydrodynamic effects of these two mouth shapes in the same animal, the bowfin fish (Amia calva). 2D Particle Image Velocimetry (PIV) is used to analyze suction feeding events. Post-processing algorithms have been developed to determine the flow rate of water into the mouth of the fish; the area of fluid, the velocity of fluid and the volume of fluid affected by the fish; the velocity of the fluid at the mouth, as well as the velocity of the fluid as a function of the distance from the mouth, finally the force exerted on the fluid by the fish is also determined. Lastly, a numerical model has been developed for comparison using a non-uniform mesh, which adapts dynamically in space and time to the fish feeding event. The realistic geometry of the fish's head is modeled in CAD. [Preview Abstract] |
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F1.00011: Bacterial accumulation mediated by flow compression-expansion Gast\'on L. Mi\~no, Ernesto Altshuler, Anke Lindner, Roman Stocker, Carlos A. Condat, Adolfo J. Banchio, Veronica I. Marconi, Eric Cl\'ement Swimming bacteria can be concentrated using a suitable microfluidic device. The combination of flow rate and surface shape can have significant impact on the microorganisms' behavior. In those processes rheotaxis, accumulation caused by ratchets and even attachment to surfaces leading biofilm formation can be observed. Under these conditions, the transport of the active suspension is deeply modified, and differs significantly from passive suspensions. In this work, we present experimental evidence of \emph{Escherichia coli} suspension flowing in a straight channel with a funnel-like constriction in the middle. This constriction is characterized by the aperture ($w_f$) and its angle ($\Theta _f$). We explore how the modification of $w_f$ and $\Theta _f$ affects the accumulation of bacteria in the channel. Concentrations of bacteria passing the constriction were observed for all the cases. However, the range of the flow rate that produced such accumulation varied with the geometry. In order to obtain a better understanding of this phenomenon, experiments are compared with a simple phenomenological model. [Preview Abstract] |
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F1.00012: On the Evolution of Pulsatile Flow Subject to a Transverse Impulse Body Force Giuseppe Di Labbio, Zahra Keshavarz-Motamed, Lyes Kadem In the event of an unexpected abrupt traffic stop or car accident, automotive passengers will experience an abrupt body deceleration. This may lead to tearing or dissection of the aortic wall known as Blunt Traumatic Aortic Rupture (BTAR). BTAR is the second leading cause of death in automotive accidents and, although quite frequent, the mechanisms leading to BTAR are still not clearly identified, particularly the contribution of the flow field. As such, this work is intended to provide a fundamental framework for the investigation of the flow contribution to BTAR. In this fundamental study, pulsatile flow in a three-dimensional, straight pipe of circular cross-section is subjected to a unidirectional, transverse, impulse body force applied on a strictly bounded volume of fluid. These models were simulated using the Computational Fluid Dynamics (CFD) software FLUENT. The evolution of fluid field characteristics was investigated during and after the application of the force. The application of the force significantly modified the flow field. The force induces a transverse pressure gradient causing the development of secondary flow structures that dissipate the energy added by the acceleration. Once the force ceases to act, these structures are carried downstream and gradually dissipate their excess energy. [Preview Abstract] |
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F1.00013: Simulation of flow in the microcirculation using a hybrid Lattice-Boltzman and Finite Element algorithm Andres Gonzalez-Mancera, Diego Gonzalez Cardenas Flow in the microcirculation is highly dependent on the mechanical properties of the cells suspended in the plasma. Red blood cells have to deform in order to pass through the smaller sections in the microcirculation. Certain deceases change the mechanical properties of red blood cells affecting its ability to deform and the rheological behaviour of blood. We developed a hybrid algorithm based on the Lattice-Boltzmann and Finite Element methods to simulate blood flow in small capillaries. Plasma was modeled as a Newtonian fluid and the red blood cells' membrane as a hyperelastic solid. The fluid-structure interaction was handled using the immersed boundary method. We simulated the flow of plasma with suspended red blood cells through cylindrical capillaries and measured the pressure drop as a function of the membrane's rigidity. We also simulated the flow through capillaries with a restriction and identify critical properties for which the suspended particles are unable to flow. The algorithm output was verified by reproducing certain common features of flow int he microcirculation such as the Fahraeus-Lindqvist effect. [Preview Abstract] |
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F1.00014: Predicting Weight Support Based on Wake Measurements of a Flying Bird in Still Air Eric Gutierrez, David Lentink The wake development of a freely flying Pacific Parrotlet (\textit{Forpus coelestis}) was examined in still air. The bird was trained to fly from perch to perch through the laser sheet while wearing custom-made laser safety goggles. This enabled a detailed study of the evolution of the vortices shed in its wake using high-speed particle image velocimetry at 1000Hz in the plane transverse to the flight path. The measurement started when the bird was approximately 0.25 wingbeats in front of the laser sheet and stopped after it traveled 3.5 wingbeats beyond the laser sheet. The instantaneous lift force that supports body weight was calculated based on the velocity field, using both the Kuttta-Joukowski and the actuator disk quasi-steady model. During the first few flaps, both models predict an instantaneous lift that is reasonably close to the weight of the bird. Several flaps away from the laser sheet, however, the models predict that the lift steadily declines to about 50{\%} of the weight of the bird. In contrast to earlier reports for bat wakes in wind tunnels, these findings for bird wakes in still air suggest that the predictive strength of quasi-steady force calculations depends on the distance between the animal and the laser sheet. [Preview Abstract] |
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F1.00015: \textit{In vivo} measurement of aerodynamic weight support in freely flying birds David Lentink, Andreas Haselsteiner, Rivers Ingersoll Birds dynamically change the shape of their wing during the stroke to support their body weight aerodynamically. The wing is partially folded during the upstroke, which suggests that the upstroke of birds might not actively contribute to aerodynamic force production. This hypothesis is supported by the significant mass difference between the large pectoralis muscle that powers the down-stroke and the much smaller supracoracoideus that drives the upstroke. Previous works used indirect or incomplete techniques to measure the total force generated by bird wings ranging from muscle force, airflow, wing surface pressure, to detailed kinematics measurements coupled with bird mass-distribution models to derive net force through second derivatives. We have validated a new method that measures aerodynamic force \textit{in vivo} time-resolved directly in freely flying birds which can resolve this question. The validation of the method, using independent force measurements on a quadcopter with pulsating thrust, show the aerodynamic force and impulse are measured within 2{\%} accuracy and time-resolved. We demonstrate results for quad-copters and birds of similar weight and size. The method is scalable and can be applied to both engineered and natural flyers across taxa. [Preview Abstract] |
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F1.00016: Roll Dynamics in a Free Flying Dragonfly James Melfi, Anthony Leonardo, Z. Jane Wang Dragonflies are capable of executing fast turning maneuvers. A typical free-flight maneuver includes rotations in all three degrees of freedom; yaw, pitch, and roll. This makes it difficult to identify the key changes to wing kinematics responsible for controlling each degree of freedom. Therefore we focus on a single motion; roll about the body longitudinal axis in a combined experimental and computational study. To induce rolling, a dragonfly is released from a magnetic tether while inverted. Both wing and body kinematics are recorded using multiple high speed cameras. The kinematics are replayed in a computer simulation of the flight, with forces and torques based on quasi-steady aerodynamics. By examining the effect of each kinematic change individually, we determine the key changes a dragonfly uses to both instigate, maintain, and end a rolling motion. [Preview Abstract] |
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F1.00017: BUBBLES, INTERFACES AND MULTIPHASE FLOWS |
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F1.00018: Analytical solution for linear long water waves, propagating in divergent channels Agust\'In Mora, Eric Bautista, Oscar Bautista, Jos\'e Hern\'andez In this work, we obtain an analytical solution for the deformation of linear long water waves, propagating in a divergent channel of slowly varying crosssection, whose width of the channel obey a power-law distribution. By using an order of magnitude analysis and proposing characteristics lengths, the nonlinear governing equations of shallow water waves are simplified and written in dimensionless form. We derive a dimensionless wave equation that predicts the surface elevation, which is solved by using a novel technique which has the purpose on seeking the appropriate Bernoulli equation of the Boundary Value Problem studied. The analytical solution thus obtained is a function of two dimensionless parameters: a kinematical parameter, $\kappa _{2} $, which is the ratio of the wavelength to the channel length and one geometrical parameter $\Gamma $, which is the ratio of the width of region$R_{1} $ to the width of region $R_{3} $. The present analytical solution, covers a wide range of linear long water waves, spreading in long divergent channels with different geometrical transitions. For values of the parameter $\Gamma >1$ the channels proposed in the present work, represent an efficient attenuator of linear long water waves. In addition, the application of the present mathematical model is not limited to thestudied cases in the present work, because the methodology used here can be extended to more complex channel transitions and also the formula presented in this work, can be easly implemented in order to validated numerical solution of long water waves. [Preview Abstract] |
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F1.00019: Large-eddy simulation of a solid-particles suspension in a turbulent boundary layer Mustafa Rahman, Ravi Samtaney We decribe a framework for the large-eddy simulation of solid particles suspended and transported within an incompressible turbulent boundary layer. The underlying approach to simulate the solid-particle laden flow is Eulerian-Eulerian in which the particles are characterized by statistical descriptors. For the fluid phase, the large-eddy simulation (LES) of incompressible turbulent boundary layer employs stretched spiral vortex subgrid-scale model and a virtual wall model similar to the work of Inoue \& Pullin (J. Fluid Mech. 2011). Furthermore, a recycling method to generate turbulent inflow is implemented. For the particle phase, the direct quadrature method of moments (DQMOM) is chosen in which the weights and abscissas of the quadrature approximation are tracked directly rather than the moments themselves. The numerical method in this framework is based on a fractional-step method with an energy-conservative fourth-order finite difference scheme on a staggered mesh. It is proposed to utilize this framework to examine transport of sand in desert sandstorms. [Preview Abstract] |
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F1.00020: ABSTRACT WITHDRAWN |
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F1.00021: Contact line dynamics on chemically heterogeneous surfaces Martin Brinkmann, Daniel Herde, Tak S. Chan, Stephan Herminghaus Modeling the dynamics of liquid interfaces in contact to heterogeneous solids involves a multitude of different length scales. A description of the unsteady motion of the three phase contact line on substrates with spatially varying wettability remains a challenging task, even for highly viscous liquids. To investigate this problem in the framework of continuum mechanics, we first consider the motion of an effectively two-dimensional viscous droplet on a plane substrate using a boundary element method to numerically solve the Steady Stokes equation. A dynamic bistability is observed on a smooth, sinusoidal wettability pattern if the magnitude of the slip length is comparable to the height of the droplet and, at the same time, the extension of the droplet is close to a multiple of the wavelength of the pattern. Employing a linear response formalism we study the complementary case of a liquid interface forced to move over the substrate at a fixed average velocity. The stick slip motion of the contact line amounts to an additional viscous dissipation close to the contact line and, hence, causes the macroscopic dynamic contact angle to increase further in the presence of spatially heterogeneous surface energies. [Preview Abstract] |
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F1.00022: Lateral migration of a spherical particle in square channel flows Masako Sugihara-Seki, Naoto Nakagawa, Atsushi Kase, Ryoko Otomo, Masato Makino, Tomoaki Itano Particles suspended in the Poiseuille flow through circular cylindrical tubes have been known to migrate perpendicular to the flow direction due to the inertial effect and to be focused toward an equilibrium radial position. Recently, the distributions of neutrally buoyant spherical particles were measured in square channel flows and it was reported that there are eight equilibrium positions of the particles in the channel cross-section, located near the centers of the channel faces and near the channel corners (Miura et al. JFM 749, 320-330, 2014). The present study is aimed to simulate numerically the motion of a spherical particle suspended in square channel flows for the channel Reynolds number (Re) up to 1000. The computation of lateral forces exerted on the particle indicated the presence of equilibrium positions at the center of the channel faces and at the channel corners. The channel corner equilibrium positions were found to be unstable for low Re, whereas the channel face equilibrium positions are always stable. As Re increases, the channel corner equilibrium positions are shifted toward the channel corner, while the channel face equilibrium positions are shifted toward the channel center. These results account for the experimental measurements. [Preview Abstract] |
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F1.00023: Solid intruders falling into foams Andr\'es P\'erez, Salom\'on \'Alvarez, Florencio S\'anchez, Ignacio Carvajal, Abraham Medina We have made experiments where we follow the trajectory of solid spherical intruders falling, due to the gravity action, in vertical rectangular acrylic-box, brimful of foam. Through this method, we can measure the mean bubble size and the effective resistance of a given foam. We found that effective resistances are very different among the cases when the foams were made in boxes open to atmosphere or in closed boxes. [Preview Abstract] |
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F1.00024: ABSTRACT WITHDRAWN |
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F1.00025: Diffuse-interface modeling of liquid-vapor coexistence in equilibrium drops using smoothed particle hydrodynamics Jaime Klapp, Leonardo Di G Sigalotti, Jorge Troconis, Eloy Sira, Franklin Pena We study numerically liquid-vapor phase separation in two-dimensional, nonisothermal, van der Waals (vdW) liquid drops using the method of Smoothed Particle Hydrodynamics (SPH). In contrast to previous SPH simulations of drop formation, our approach is fully adaptive and follows the diffuse interface model for a single-component fluid, where a reversible, capillary (Korteweg) force is added to the equations of motion to model the rapid but smooth transition of physical quantities through the interface separating the bulk phases. Surface tension arises naturally from the cohesive part of the vdW equation of state and the capillary forces. The drop models all start from a square-shaped liquid and spinodal decomposition is investigated for a range of initial densities and temperatures. The simulations predict the formation of stable, subcritical liquid drops with a vapor atmosphere, with the densities and temperatures of coexisting liquid and vapor in the vdW phase diagram closely matching the binodal curve. We find that the values of surface tension, as determined from the Young-Laplace equation, are in good agreement with the results of independent numerical simulations and experimental data. The models also predict the increase of the vapor pressure with temperature and the fitting to the numerical data reproduces very well the Clausius-Clapeyron relation, thus allowing for the calculation of the vaporization pressure for this vdW fluid. [Preview Abstract] |
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F1.00026: Compressible bubbly shock problem: Revisited Asha Chigurupati, Sanjiva Lele The problem of shock waves in bubbly flows has been studied in great depth and is a part of an extensive body of literature. Most of this literature assumes the liquid to be incompressible. In this study, we look at the problem of shock waves in bubbly flows where liquid is treated as compressible. A simple 1-D flow problem is considered to study the effect of liquid compressibility on shock speed. The results obtained show higher values of shock speeds for incompressible case when compared to compressible case. This difference is negligible for higher void fractions (of the order of 10\textasciicircum -1) but grows immensely as you decrease the void fractions further by several orders of magnitude. Results pertaining to the structure and propagation of shock waves, particularly in this range of void fractions, will be presented. Future investigations will focus on studying the accompanying bubble-bubble interactions and looking at transient solutions of the problem. [Preview Abstract] |
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F1.00027: Lattice Boltzmann simulation of self-driven bubble transport in a micro-channel with a virtual check valve Rou Chen, Wei Diao, Yongguang Cheng, Likun Zhu, Huidan (Whitney) Yu An innovative self-circulation, self-regulation mechanism has recently been proposed to experimentally generate gaseous species from liquid reactants with little or zero parasitic power consumption. When a bubble grows at a location close to a virtual check valve, expansion of the left meniscus of the bubble is hindered due to its capability to provide a higher capillary pressure than the right meniscus does. We perform numerical simulation of bubble transport in a channel with a virtual check valve using lattice Boltzmann method to provide benchmarks for the experiments. A stable discretized lattice Boltzmann equation is employed to simulate incompressible bubble-liquid flows with density ratio above 1000. Polynomial wall free energy boundary condition is introduced and examined for static cases with a bubble sitting on solid surfaces for a triple contact among bubble, liquid, and solid surface. In this work, we focus on the effects of channel ratio between with and without check valve on the dynamics of bubble-driven liquid circulation. [Preview Abstract] |
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F1.00028: Dynamics of skirting droplets Caleb Akers, Jacob Hale It has been observed that non-coalescence between a droplet and pool of like fluid can be prolonged or inhibited by sustained relative motion between the two fluids. In this study, we quantitatively describe the motion of freely moving droplets that skirt across the surface of a still pool of like fluid. Droplets of different sizes and small Weber number were directed horizontally onto the pool surface. After stabilization of the droplet shape after impact, the droplets smoothly moved across the surface, slowing until coalescence. Using high-speed imaging, we recorded the droplet's trajectory from a top-down view as well as side views both slightly above and below the fluid surface. The droplets' speed is observed to decrease exponentially, with the smaller droplets slowing down at a greater rate. Droplets infused with neutral density micro beads showed that the droplet rolls along the surface of the pool. A qualitative model of this motion is presented. [Preview Abstract] |
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F1.00029: A boundary element method for particle and droplet electrohydrodynamics in the Quincke regime Debasish Das, David Saintillan Quincke electrorotation is the spontaneous rotation of dielectric particles suspended in a dielectric liquid of higher conductivity when placed in a sufficiently strong electric field. This phenomenon of Quincke rotation has interesting implications for the rheology of these suspensions, whose effective viscosity can be controlled and reduced by application of an external field. While spherical harmonics can be used to solve the governing equations for a spherical particle, they cannot be used to study the dynamics of particles of more complex shapes or deformable particles or droplets. Here, we develop a novel boundary element formulation to model the dynamics of a dielectric particle under Quincke rotation based on the Taylor-Melcher leaky dielectric model, and compare the numerical results to theoretical predictions. We then employ this boundary element method to analyze the dynamics of a two-dimensional drop under Quincke rotation, where we allow the drop to deform under the electric field. Extensions to three-dimensions and to the electrohydrodynamic interactions of multiple droplets are also discussed. [Preview Abstract] |
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F1.00030: Pick up and remove particles by water droplet using dissipative particle dynamics Chuanjin Lan, Souvik Pal, Zhen Li, Yanbao Ma Particle removal is a crucial concern for many engineering processes, such as, glass cleaning and substrate cleaning, where the removal of nanoparticles is a great challenge. In order to clean the surface without causing any mechanical damage to it, we use water droplets to pick up and remove the nanoparticles. Dissipative particle dynamics simulation is used to model the interaction between the water droplet and nanoparticles, as well as the solid substrate surface. The hydrophilic nanoparticles are successfully cleaned up by water droplet, and the detailed motion of these particles together with droplet is also captured. The results show that the water droplet can be used as an efficient tool for removal of nanoparticles from a surface. [Preview Abstract] |
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F1.00031: A study of water droplet between an AFM tip and a substrate using dissipative particle dynamics Souvik Pal, Chuanjin Lan, Zhen Li, E. Daniel Hirleman, Yanbao Ma Formation of a water droplet between a sharp AFM tip and a substrate due to capillary condensation affects the tip-substrate interaction. As a consequence, AFM measurements lose precision and often produce incorrect sample topology. Understanding the physics of liquid bridges is also important in the field of Dip-pen nanolithography (DPN). Significant research is being carried out to understand the mechanics of the formation of the liquid bridge and its dependence of surface properties, ambient conditions etc. The in-between length scale, i.e., mesoscale ($\sim$ 100 nm) associated with this phenomenon presents a steep challenge for experimental measurements. In addition, molecular dynamics (MD) can be computationally prohibitive to model the entire system, especially over microseconds to seconds. Theoretical analysis using Young Laplace equation has so far provided some qualitative insights only. We study this system using Dissipative Particle Dynamics (DPD) which is a simulation technique suitable for describing mesoscopic hydrodynamic behavior of fluids. In this work, we carry out simulations to improve understanding of the process of formation of the meniscus, the mechanics of manipulation and control of its shape, and better estimation of capillary forces. The knowledge gained through our study will help in correcting the AFM measurements affected by capillary condensation. Moreover, it will improve understanding of more accurate droplet manipulation in DPN. [Preview Abstract] |
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F1.00032: CONTROL AND STABILITY |
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F1.00033: Effect of initial amplitude on the interfacial and bulk dynamics in Richtmyer-Meshkov instability under conditions of high energy density Zachary Dell, Robert Stellingwerf, Snezhana Abarzhi We systematically study the effect of the initial amplitude on the interfacial and bulk dynamics of the Richtmyer-Meshkov instability (RM) induced by strong shocks. The shock propagates from the light to the heavy fluid. The fluid densities are contrast. The fluid interface is initially perturbed with a cosine wave perturbation. Its amplitude is varied from 0\% to 100\% of the initial perturbation wavelength. A broad range of shock strengths and density ratios is considered. Smoothed particle hydrodynamics code is employed to ensure shock capturing and interface tracking. Detailed diagnostics of the flow scalar and vector fields is performed. Whenever possible the simulation results are compared with existing theoretical analyses achieving good agreement. The focus question of our study is how the energy deposited by the shock is partitioned between the interfacial and volumetric components. We analyze the dependence of the initial growth-rate of RMI, the velocity away from the interface, and the transmitted shock velocity as functions of the initial amplitude. Particularly, we found that for a Mach number 5 and an Atwood number 0.8, the initial growth rate is highest and the interfacial energy is the largest when the initial amplitude is about a quarter of the wavelength. [Preview Abstract] |
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F1.00034: Flow Instability Past A Rounded Cylinder Doohyun Park, Kyung-Soo Yang Numerical simulation of flow past a rounded cylinder has been performed to study the effects of rounding corners of an angulated cylinder on the primary (2D) and the secondary (3D) instabilities associated with the corresponding flow configuration. 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 ($r)$. Firstly, the characteristics of the primary instability such as critical Reynolds number (Re$_{c})$, force coefficients, and Strouhal number for vortex shedding are reported against $r$. It was found that Re$_{c}$ is maximum at $r/D=$0.25, meaning that this flow is more stable than the two extreme cases of the square and circular cylinders. Furthermore, there are the optimal values of $r/D$ for force coefficients, which vary with Re. Secondly, we studied the onset of 3D instabilities by using Floquet stability analysis. It turned out that the criticalities of 3D instability modes are significantly affected by $r$. [Preview Abstract] |
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F1.00035: Resolvent mode identification in a turbulent boundary layer Kevin Rosenberg, Beverley McKeon The resolvent analysis developed by McKeon and Sharma (J. Fluid Mechanics, 2010) has demonstrated a connection between the most amplified disturbances in wavenumber/frequency space and observed structures in wall turbulence. Three simultaneous hotwire measurements are made across a zero-pressure gradient turbulent boundary layer to identify the resolvent modes associated with these structures. A resolvent mode is designated by a streamwise wavenumber, a spanwise number, and a temporal frequency (k, n, $\omega $ respectively) and physically represents a travelling wave. The three wires are aligned in the wall normal direction and spaced in the streamwise and spanwise directions. The signals are filtered at the frequency corresponding to the resolvent mode of interest and ensemble averaged over a single period; the resulting phase differences between wires and their respective separation distances allows for the calculation of the spatial wavenumbers. The eventual goal is to sense these modes in real time as this will provide an important first step towards the development of closed-loop control schemes, specifically within the context of the resolvent framework. [Preview Abstract] |
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F1.00036: Feedback control for oscillation damping in cavity flow Mohamed-Yazid Rizi, Luc Pastur, Mohamed Abbas-turki, Hisham Abou-kandil, Yann Fraingneau It is well known that the cavity flow provides a benchmark configuration to understand the self-sustained oscillations of the impingement shear layer that constitutes in numerous application the first source of acoustic noise. This study is focused on the design of a closed-loop control strategy to suppress the cavity flow self-sustained oscillations. We show that a simple time-delayed feedback control law kills the limit cycle and stabilizes the steady base flow. This control law happens to be easy to implement experimentally and rather robust to changes in flow conditions. To establish a linear dynamical model representing the cavity flow, a closed-loop identification technique (Eigensystem Realization Algorithm - ERA) is used. As expected, results indicate that the oscillation frequencies of the cavity are mainly due to the unstable modes of the linear dynamics. An $H_2$ optimal controller is designed by exploiting the identified linear dynamical model. Our $H_2$ controller stabilizes the cavity oscillations and is robust to parameters variations. [Preview Abstract] |
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F1.00037: Propagations of fluctuations and flow separation on an unsteadily loaded airfoil Andrew Tenney, Jacques Lewalle We analyze pressure data from 18 taps located along the surface of a DU-96-W180 airfoil in bothand steady flow conditions. The conditions were set to mimic the flow conditions experienced by a wind turbine blade under unsteady loading to test and to quantify the effects of several flow control schemes. Here we are interested in the propagation of fluctuations along the pressure and suction sides, particularly in relation to the fluctuating separation point. An unsteady phase of the incoming fluctuations is defined using Morlet wavelets, and phase-conditioned cross-correlations are calculated. Using wavelet-based pattern recognition, individual events in the pressure data are identified with several different algorithms utilizing both the original time series pressure signals and their corresponding scalograms. The data analyzed in this study was collected by G. Wang in the Skytop anechoic chamber at Syracuse University in the spring of 2013; the work of Zhe Bai on this data is also acknowledged. [Preview Abstract] |
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F1.00038: On a possible mechanism for the generation of cyclonic vortices regime in a precessing cylindrical container Waleed Mouhali, Thierry Lehner We report experimental observations obtained by particle image velocimetry of the behavior of a flow driven by rotation and precession of a cylindrical container. Various flow regimes are identified according to the value of the control parameter $\varepsilon $ (also called the Poincar\'{e} number) which is the ratio of the precession frequency $\Omega_{\mathrm{P}}$ to the rotation frequency $\Omega_{\mathrm{R}}$. In particular, when $\varepsilon$ is increased from small values, we have observed an induced differential rotation followed by the apparition of permanent cyclonic vortices. In particular, when $\varepsilon$ is increased from small values, after a linear regime, we have observed a differential rotation followed by the apparition of four permanent cyclonic vortices as a consequence of instability (eruption of jets from the lateral edges of the cylinder). We propose a mechanism for the explanation of this generation. based on the differential rotation created by nonlinear mode coupling of two inertial waves of azimuthal wave numbers $m =$ 0 and $m =$ 1 (mode forced by the precession) in the inviscid case. The profile of the azimuthal mean velocity and the corresponding axial mean vorticity both show an inflexion point in their radial profile leading to a possible localized instability. [Preview Abstract] |
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F1.00039: BUOYANCY AND THERMAL CONVECTION |
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F1.00040: Computational investigation of negatively buoyant jets Leandre Berard, Mehdi Raessi We present computational results on the stability of negatively buoyant jets at various Richardson numbers and injection angles. The results show a critical Richardson number that is the boundary between stable and unstable behavior. The critical Richardson number is seen to vary with injection angle. The computational results also reveal the mechanisms leading to instability and shedding of oil ring structures. The computational tool is a 3D GPU-accelerated MPI-parallel two-phase flow solver. The governing equations are solved using the two-step project method in the finite volume context. The fluid interfaces are tracked using the volume-of-fluid method. The pressure Poisson solver is accelerated using GPUs, which provides an average acceleration factor of 5 in 3D parallel simulations. [Preview Abstract] |
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F1.00041: On the spiral roll state in thermal convection in spherical shell Tomoaki Itano, Takahiro Ninomiya, Keito Konno, Masako Sugihara-Seki It is found that the ``giant'' spiral roll state in thermal convection in non-rotating spherical shell with a finite Pr reported by Zhang and others (Phys.Rev.E, 2002) exists with a subtle modification under conservation of invariance of ${\cal C}_2$ symmetry even at a relatively thicker spherical shell. By means of a detail numerical bifurcation analysis with aid of direct numerical simulation for the time-development of the system, it is elucidated that this state orginates, in the parameter space, at a higher Rayleigh number but a lower azimuthal wavenumber than the set of parameters where the state previously found by Zhang exists. [Preview Abstract] |
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F1.00042: Thermal convection in a rotating horizontal annulus Alexey Vjatkin, Alevtina Ivanova, Victor Kozlov Thermal convection of viscous fluid in a coaxial horizontal gap rotating around its own axis is investigated experimentally. The temperature of inner boundary is higher than that of the outer one. The threshold of mean convection excitation is studied. It is found that, despite the stabilizing effect of the centrifugal force of inertia, the convection in the layer occurs in a threshold way at lowering the rotation velocity and is excited by thermovibrational mechanism. In viscous liquids crisis of heat transfer is associated with the appearance of vortices extended along the azimuth (three-dimensional structures), and the longitudinal two-dimensional rolls appear on the background of them. In the experiments with low-viscosity fluids the opposite sequence of convective processes development is observed. With the advent of convective structures their slow azimuthal drift relative to the cavity is registered. It is shown that the drift is associated with the azimuthal steady motion of the fluid, which is generated in Stokes layers near the boundaries. The increase of viscosity results in growth of wavelength of the longitudinal rolls and significant reduction of the velocity the drift of vortex system. Experimental results agree with theoretical predictions. [Preview Abstract] |
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F1.00043: Comparison of CFD simulation of night purge ventilation to full-scale building measurements Asha Chigurupati, Catherine Gorle, Gianluca Iaccarino Efforts to improve the understanding of air motion in and around buildings can lead to more efficient natural ventilation systems, thereby significantly reducing a building's heating and cooling demands. CFD simulations enable solving the details of the flow and convective heat transfer in buildings and have the potential to predict the performance of natural ventilation with a high degree of accuracy. Understanding the actual predictive capability of CFD simulations is however complicated by the complexity of the geometry and physics involved, and the uncertainty and variability in the boundary conditions. In the present study we model the night flush process in the Y2E2 building on Stanford University's campus and compare the results to measurements in the full-scale, operational building. We model half of the building, which consists of three floors with office spaces and two atriums. We solve the RANS equations using ANSYS/Fluent and k-e RNG theory turbulence closure model for the duration of one night flush and will present a comparison of the CFD results to measurements of the temperature on each floor in both atriums. Future investigations will focus on the potential of reducing the discrepancy between observed and predicted values by varying uncertain model parameters and boundary conditions. [Preview Abstract] |
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F1.00044: TURBULENCE |
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F1.00045: Identification of Coherent Structures in Premixed Reacting Flows Eileen Haffner, Melissa Green, Elaine Oran Many studies have been conducted on the best ways to quantitatively characterize the turbulence-flame interaction in reacting flows. It has been observed that increased turbulence intensity both wrinkles and broadens the flame front throughout the preheat zone and reaction zone. A Lagrangian coherent structures analysis is used to identify the individual coherent turbulent structures as the maximizing ridges of the Finite-Time Lyapunov exponent scalar field (FTLE). This method provides different information than Eulerian criteria which have predominantly been used in previous reacting flow studies. Preliminary results show that LCS ridges exhibit a clear qualitative correlation to the contour of the fuel mass-fraction of the flame. A quantitative characterization of how the LCS results correlate to observed flame geometries will allow for a better understanding of how these structures affect the flame brush, and could lead to improved efficiency in particular engines. [Preview Abstract] |
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F1.00046: Large-eddy simulations of the restricted nonlinear system Joel Bretheim, Dennice Gayme, Charles Meneveau Wall-bounded shear flows often exhibit elongated flow structures with streamwise coherence (e.g. rolls/streaks), prompting the exploration of a streamwise-constant modeling framework to investigate wall-turbulence. Simulations of a streamwise-constant (2D/3C) model have been shown to produce the roll/streak structures and accurately reproduce the blunted turbulent mean velocity profile in plane Couette flow. The related restricted nonlinear (RNL) model captures these same features but also exhibits self-sustaining turbulent behavior. Direct numerical simulation (DNS) of the RNL system results in similar statistics for a number of flow quantities and a flow field that is consistent with DNS of the Navier-Stokes equations. Aiming to develop reduced-order models of wall-bounded turbulence at very high Reynolds numbers in which viscous near-wall dynamics cannot be resolved, this work presents the development of an RNL formulation of the filtered Navier-Stokes equations solved for in large-eddy simulations (LES). The proposed LES-RNL system is a computationally affordable reduced-order modeling tool that is of interest for studying the underlying dynamics of high-Reynolds wall-turbulence and for engineering applications where the flow field is dominated by streamwise-coherent motions. [Preview Abstract] |
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F1.00047: Wall-Resolved Large-Eddy Simulation of Turbulent Flow Past a NACA0012 Airfoil Wei Gao, Wei Zhang, Ravi Samtaney Large-eddy simulation (LES) of turbulent flow past a NACA0012 airfoil is performed at angle of attack (AoA) $3^o$ and $Re_c=2.3 \times 10^4$. The filtered incompressible Navier-Stokes equations are spatially discretized using an energy conservative fourth-order scheme developed by Morinishi {\it et al}. (J. of Comput. Phys., 1998), and the subgrid-scale (SGS) tensor is modeled by the stretched-vortex SGS model developed by Pullin and co-workers (Phys. of Fluids, 2000, J. of Fluid Mech., 2009). An extension of the original stretched-vortex SGS model is utilized to resolve the streak-like structures in the near-wall flow regions. The mean velocity and turbulence intensity profiles on airfoil surface and in wake are validated against experimental data reported in Dong-Ha Kim {\it et al.} (AIAA, 2009). To further verify our LES capacity, some high-order turbulence quantities are also compared with the DNS results produced by our in-house DNS code. The effect of grid-refinement on the wall-resolved LES approach is also discussed. [Preview Abstract] |
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F1.00048: Spectral analysis of structure functions and their scaling exponents in forced isotropic turbulence Moritz Linkmann, W. David McComb, Samuel Yoffe, Arjun Berera The pseudospectral method, in conjunction with a new technique for obtaining scaling exponents $\zeta_n$ from the structure functions $S_n(r)$, is presented as an alternative to the extended self-similarity (ESS) method and the use of generalized structure functions. We propose plotting the ratio $|S_n(r)/S_3(r)|$ against the separation $r$ in accordance with a standard technique for analysing experimental data. This method differs from the ESS technique, which plots the generalized structure functions $G_n(r)$ against $G_3(r)$, where $G_3(r) \sim r$. Using our method for the particular case of $S_2(r)$ we obtain the new result that the exponent $\zeta_2$ decreases as the Taylor-Reynolds number increases, with $\zeta_2 \to 0.679 \pm 0.013$ as $R_\lambda \to \infty$. This supports the idea of finite-viscosity corrections to the K41 prediction for $S_2$, and is the opposite of the result obtained by ESS. The pseudospectral method permits the forcing to be taken into account exactly through the calculation of the energy input in real space from the work spectrum of the stirring forces. The combination of the viscous and the forcing corrections as calculated by the pseudospectral method is shown to account for the deviation of $S_3$ from Kolmogorov's ``four-fifths''-law at all scales. [Preview Abstract] |
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F1.00049: Investigation of electric charge on inertial particle dynamics in turbulence Jiang Lu, Raymond Shaw The behavior of electrically charged, inertial particles in homogeneous, isotropic turbulence is investigated. Both like-charged and oppositely-charged particle interactions are considered. Direct numerical simulations (DNS) of turbulence in a periodic box using the pseudospectral numerical method are performed, with Lagrangian tracking of the particles. We study effects of mutual electrostatic repulsion and attraction on the particle dynamics, as quantified by the radial distribution function (RDF) and the radial relative velocity. For the like-charged particle case, the Coulomb force leads to a short range repulsion behavior and an RDF reminiscent of that for a dilute gas. For the oppositely-charged particle case, the Coulomb force increases the RDF beyond that already occurring for neutral inertial particles. For both cases, the relative velocities are calculated as a function of particle separation distance and show distinct deviations from the expected scaling within the dissipation range. [Preview Abstract] |
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F1.00050: Statistical Modeling of Epistemic Uncertainty in RANS Turbulence Models Iman Rahbari, Vahid Esfahanian RANS turbulence models are widely used in industrial applications thanks to their low computational costs. However, they introduce model-form uncertainty originating from eddy-viscosity hypothesis, assumptions behind transport equations of turbulent properties, free parameters in the models, and wall functions. In contrast, DNS provides detailed and accurate results but in high computational costs making it unaffordable in industrial uses. Therefore, quantification of structural uncertainty in RANS models using DNS data could help engineers to make better decisions from the results of turbulence models. In this study, a new and efficient method for statistical modeling of uncertainties in RANS models is presented, in which deviation of predicted Reynolds stress tensor from results of DNS data is modeled through a Gaussian Random Field. A new covariance kernel is proposed based on eigendecomposition of a sample kernel, hyperparameters are found by minimization of negative log likelihood employing Particle Swarm Optimization algorithm. Thereafter, the random field is sampled using Karhunen-Loeve expansion followed by solving RANS equations to obtain the quantity of interest for each sample as uncertainty propagation. In the present study, fully developed channel flow as well as flow in a converging-diverging channel are considered as test cases. [Preview Abstract] |
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F1.00051: Turbulent Flow Over a Low-Camber Pitching Arc Wing Majid Molki Aerodynamics of pitching airfoils and wings are of great importance to the design of air vehicles. This investigation presents the effect of camber on flow field and force coefficient for a pitching circular-arc airfoil. The wing considered in this study is a cambered plate of zero thickness which executes a linear pitch ramp, hold and return of 45$\,^{\circ}$ amplitude. The momentum equation is solved on a mesh that is attached to the wing and executes a pitching motion with the wing about a pivot point located at 0.25-chord or 0.50-chord distance from the leading edge. Turbulence is modeled by the $k-\omega$ SST model. Using the open-source software OpenFOAM, the conservation equations are solved on a dynamic mesh and the flow is resolved all the way to the wall ($y^+\approx 1$). The computations are performed for Re = 40,000 with the reduced pitch rate equal to $K=c\dot{\theta}/{2U_{\infty}} = 0.2$. The results are presented for three wings, namely, a flat plate (zero camber) and wings of 4\% and 10\% camber. It is found that the flow has complex features such as leading-edge vortex, near-wake vortex pairs, clockwise and counter-clockwise vortices, and trailing-edge vortex. While vortices are formed over the flat plate, they are formed both over and under the cambered wing. [Preview Abstract] |
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F1.00052: Ahmad Reza Estakhr Number, (Fluid Dynamics) Ahmad Reza Estakhr The Estakhr Number is a dimensionless number defined as: $E_n=\frac{\lambda}{\eta}$ where $\lambda$ denotes mean free path and $\eta$ denotes Kolmogorov length scale. The Mach and Estakhr Numbers are therefore related by: $E_n=Ma\sqrt{\frac{\gamma\pi}{2}}$ where the $Ma$ denotes Mach number, $\gamma$ denotes the ratio of specific heats and is dimension less. At high Reynolds number the Knudsen, Estakhr and Reynolds Numbers are therefore related by: $E_n=K_nR_e$ where the $K_n$ denotes Knudsen number and $R_e$ denotes Reynolds number. [Preview Abstract] |
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F1.00053: NUMERICAL SIMULATIONS |
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F1.00054: Shock interaction behind a pair of cylindrical obstacles Heng Liu, Raoul Mazumdar, Veronica Eliasson The body of work focuses on two-dimensional numerical simulations of shock interaction with a pair of cylindrical obstacles, varying the obstacle separation and incident shock strength. With the shock waves propagating parallel to the center-line between the two cylindrical obstacles, the shock strengths simulated vary from a Mach of 1.4 to a Mach of 2.4, against a wide range of obstacle separation distance to their diameters. These cases are simulated via a software package called Overture, which is used to solve the inviscid Euler equations of gas dynamics on overlapping grids with adaptive mesh refinement. The goal of these cases is to find a so-called ``safe'' region for obstacle spacing and varying shock Mach numbers, such that the pressure in the ``safe'' region is reduced downstream of the obstacles. The benefits apply to both building and armor design for the purpose of shock wave mitigation to keep humans and equipment safe. The results obtained from the simulations confirm that the length of the ``safe'' region and the degree of shock wave attenuation depend on the ratio of obstacle separation distance to obstacle diameter. The influence of various Mach number is also discussed. [Preview Abstract] |
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F1.00055: High-Order Ghost-Fluid Method for Compressible Flow in Complex Geometry Mohamad Al Marouf, Ravi Samtaney We present a high-order embedded boundary method for numerical solutions of the Compressible Navier Stokes (CNS) equations in arbitrary domains. A high-order ghost fluid method based on the PDEs multidimensional extrapolation approach of Aslam (J. Comput. Phys. 2003) is utilized to extrapolate the solution across the fluid-solid interface to impose boundary conditions. A fourth order accurate numerical time integration for the CNS is achieved by fourth order Runge-Kutta scheme, and a fourth order conservative finite volume scheme by McCorquodale \& Colella (Comm. in App. Math. \& Comput. Sci. 2011) is used to evaluate the fluxes. Resolution at the embedded boundary and high gradient regions is accomplished by applying block-structured adaptive mesh refinement. A number of numerical examples with different Reynolds number for a low Mach number flow over an airfoil and circular cylinder will be presented. [Preview Abstract] |
(Author Not Attending)
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F1.00056: Momentum equations of Newtonian fluids fully in the Eulerian perspective Qifeng Lv, Sijing Wang, Moran Wang The Navier-Stokes equations are used to describe the flow of Newtonian fluids in the Eulerian perspective. However, we find the right-hand sides of the Navier-Stokes equations were derived not from the Eulerian perspective but rather from the Lagrangian perspective, although this makes the Navier-Stokes equations simple and also valid in the laminar flow. In fact, the Lagrangian Cauchy strain rates were used in the derivation of the Navier-Stokes equations. Thus, here we derive the Cauchy strain rates from the Eulerian perspective. We then find the difference between the Eulerian and the Lagrangian Cauchy strain rates cannot be neglected when in turbulent flows or compressible fluid flows. Thereby, On the basis of the Eulerian Cauchy strain rates, we derive a set of momentum equations for the flow of Newtonian fluids fully in the Eulerian perspective. [Preview Abstract] |
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F1.00057: MICRO AND NANO FLUID DYNAMICS |
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F1.00058: Dimensionless numbers describing the onset of flow transitions in flow-focusing and T-junction microfluidic devices Siva Vanapalli, Jihay Kim, Mehdi Nekouei T-junction and flow focusing geometries are the most commonly used drop generators in microfluidic devices. Several studies have documented the different behaviors of dispersed phase in these devices including break-up modes such as squeezing, dripping, and jetting and a non-break-up mode involving co-flowing laminar streams, called parallel stream. However, the control parameters that govern the transitions between these behaviors are not fully known. Using a combination of experiments and numerical simulations, we find that the onset of the dispersed phase transitions can be described by two dimensionless numbers -- Weber number based on outer phase and Reynolds number based on the inertia of the inner phase and viscous stress of the outer phase. The flow transition from drop regime to jetting occurs at We$_{\mathrm{o}}$ $\sim$ O(1), and the flow transition from drop regime to parallel stream occurs at Re* $\sim$ 1. This scaling of flow transition was not affected by the change in the viscosity ratio, concentration of surfactant, the height of the channel, and the wettability of the device. Thus, our studies suggest that these two dimensionless numbers capture the onset of flow transitions in microfluidic drop generators. [Preview Abstract] |
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F1.00059: Study on three-dimensional printing using electrohydrodynamic inkjet by analysis of mass flow rate Han Seo Ko, Soo-Hong Lee, Pil-Ho Lee, Sang Won Lee An electrohydrodynamic (EHD) jet can produce much smaller droplets than nozzle sizes even for highly viscous liquid. Micro scale patterns are produced by a direct patterning of the EHD inkjet printing technique to obtain lamination layers. A cone-jet mode shows good performance for line and surface printings. A prediction method for a flow rate was proposed by performing experiments and deriving an equation. The calculation was carried out by dividing the electric field and the fluid regions. Dielectric liquids were used as the working fluid, whose flow rate was measured at the applied voltage of 1.5kV to 2.5kV. The measured flow rate was affected by viscosity, surface tension, and density as fluid properties, and dielectric constant and electric conductivity as properties of electric fields for the voltage. Then, parameters of the printing were investigated by printed line width and thickness at various conditions. As a result, the applied static pressure had more effect on the line printing although the line width was affected by the stage velocity. The significant role of the parameters was confirmed to produce scaffolds using the three-dimensional EHD printing. [Preview Abstract] |
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F1.00060: Direct patterning using aerodynamically assisted electrohydrodynamic jet printing Sangyeon Hwang, Baekhoon Seong, Wonyoung Lee, Doyoung Byun Electrical force and aerodynamic force are considered to be preferred sources for generating a liquid jet to emit the target fluid on a tiny scale. The former is known as an electrohydrodynamic (EHD) jet, while the latter is called flow focusing. Here, we report the effect of a combined energy source on the micro scale jet and patterns and investigate the scaling law of pattern width according to the ratio of two energy sources. In a conventional EHD jet, after a short length of straight section the charged viscous jet turns into complex shape which occurs difficulty in patterning fine lines. A coaxially driven gas stream smoothed the asymmetric jet lengthening the straight section of the jet. The jet could be issued constantly within the range that did not exceed the stable region in the parametric space. Under such stable conditions, the jet became narrow as compared to the one from the normal EHD jet. Hence, the patterns formed at a high gas pressure were noticeably smaller than the others, demonstrating the controllability of jet thickness. Various liquids had been used as the target fluids to investigate the effect of liquid properties. [Preview Abstract] |
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F1.00061: Capillary penetration of a liquid between two tilted plates making a small angle Abel Lopez-Villa, Francisco Higuera, Aydet Jara, Sergio de Santiago, Abraham Medina The penetration of a wetting liquid in the narrow gap between two tilted plates making a small angle is analyzed in the framework of the lubrication approximation. At the beginning of the process, the liquid rises independently at different distances from the line of intersection of the plates except in a small region around this line where the effect of the gravity is negligible. The maximum height of the liquid initially increases as a function of time and the angle of inclination. At later times, the motion of the liquid is confined to a thin layer around the line of intersection whose height increases as a power of time. The evolution of the liquid surface is computed numerically and compared with the results of a simple experiment. [Preview Abstract] |
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F1.00062: Dynamics of hemiwicking Jungchul Kim, Ildoo Kim, Ho-Young Kim We study the wicking dynamics of a liquid on a surface decorated with micropillars, which has been long known to be governed by the Washburn-like dynamics. However, rough substrates cannot be described by a single geometric parameter like a tube with a constant radius. So far, different forms of scaling laws for liquid propagation distance were suggested by different researchers, but most of the laws are valid for the specific experimental conditions (e.g. pillar aspect ratio) employed in each work. Here we propose a novel scaling law for the wetting speed as a function of the width, gap, and height of the pillars, and the physicochemical liquid properties, which is valid for considerably wide parameter space. Also, we discuss the maximum pillar spacing up to which the current assumption of densely spaced pillars is valid. [Preview Abstract] |
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F1.00063: Numerical study of dynamic behavior of contact line approaching a micro-scale particle Yusuke Miyazaki, Takahiro Tsukahara, Ichiro Ueno The behavior of contact line (CL) the boundary line of solid-liquid-gas interface is one of the important topics regarding the dynamic wetting. Many experimental and theoretical approaches have been performed about static and axisymmetric systems: e.g., Ally et al. (Langmuir 2010 vol. 26, 11797) measured the capillary force on a micro-scale particle attached to a liquid surface and they compared with their physical model. However, there are few numerical simulations of the dynamic and asymmetric systems Focusing on the CL passing micro-scale solid particles, we simulated solid-liquid-gas flows. Gas-liquid interface is captured by a VOF method and the surface tension model is the CSF model. Solid-fluid interaction is treated by an immersed boundary method. We studied the broken-dam problem with a fixed sphere in either macro or micro scale. Our results of the macro scale agree reasonably with the experimental result. In the micro scale, where the domain is of 2.0 $\times$ 2.0 $\times$ 2.0 $\mu $m$^{3}$ and the sphere diameter is 0.5 $\mu $m, we tested two types of sphere surface: hydrophobic and hydrophilic solids. We demonstrated that, as the liquid touches the hydrophilic sphere, the velocity of CL is higher than the hydrophobic case. [Preview Abstract] |
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F1.00064: A Two-Stage Microfluidic Device for the Isolation and Capture of Circulating Tumor Cells Andrew Cook, Sayali Belsare, Todd Giorgio, Richard Mu Analysis of circulating tumor cells (CTCs) can be critical for studying how tumors grow and metastasize, in addition to personalizing treatment for cancer patients. CTCs are rare events in blood, making it difficult to remove CTCs from the blood stream. Two microfluidic devices have been developed to separate CTCs from blood. The first is a double spiral device that focuses cells into streams, the positions of which are determined by cell diameter. The second device uses ligand-coated magnetic nanoparticles that selectively attach to CTCs. The nanoparticles then pull CTCs out of solution using a magnetic field. These two devices will be combined into a single 2-stage microfluidic device that will capture CTCs more efficiently than either device on its own. The first stage depletes the number of blood cells in the sample by size-based separation. The second stage will magnetically remove CTCs from solution for study and culturing. Thus far, size-based separation has been achieved. Research will also focus on understanding the equations that govern fluid dynamics and magnetic fields in order to determine how the manipulation of microfluidic parameters, such as dimensions and flow rate, will affect integration and optimization of the 2-stage device. [Preview Abstract] |
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F1.00065: Non-linear dynamics of viscous bilayers subjected to an electric field: 3D phase field simulations Christos Dritselis, George Karapetsas, Vasilis Bontozoglou The scope of this work is to investigate the non-linear dynamics of the electro-hydrodynamic instability of a bilayer of immiscible liquids. We consider the case of two viscous films which is separated from the top electrode by air. We assume that the liquids are perfect dielectrics and consider the case of both flat and patterned electrodes. We develop a computational model using the diffuse interface method and carry out 3D numerical simulations fully accounting for the flow and electric field in all phases. We perform a parametric study and investigate the influence of the electric properties of fluids, applied voltage and various geometrical characteristics of the mask. [Preview Abstract] |
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F1.00066: Self-assembly of nanoparticles in evaporating particle-laden emulsion drops Min Pack, Xin Yang, Ying Sun In this study, we demonstrate the scalable fabrication of nanostructures (e.g., nanomesh and nanoring arrays) via inkjet printing of oil-in-water emulsion drops containing nanoparticles in water. Nanoscale oil drops dispersed in water are used here as templates for assembly of nanoparticles on a substrate. The effect of oil vapor pressure on particle deposition morphologies is studied by using a variety of oils. For oil drops with a lower vapor pressure, non-uniform evaporation rate along the air-water interface drives dispersed oil drops to move and accumulate near the air/water/substrate contact line. These oil drops remain on the substrate while water is evaporating enabling nanoparticles to self-assemble into nanomeshes. While keeping the same oil concentration, oil drops with a higher vapor pressure completely evaporates near the contact line before water dries out, leading to nanoparticle deposition of coffee-ring structures. If nanoparticles are confined inside the dispersed oil drops, nanoring arrays are formed as the emulsion evaporates. The characteristics of the nanomeshes and nanorings are controlled by tuning the size and concentration of oil drops and nanoparticles, substrate wettability, surfactant concentration, and vapor pressure of oil. [Preview Abstract] |
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F1.00067: FIB design for nano-fluidic applications Remy Fulcrand, Alessandro Siria, Anne-Laure Biance, Lyderic Bocquet In this paper we briefly review the techniques available to researchers in the nano-fluidic domain to fabricate nano-pores and nano-channels. In this context the focused ion beam (FIB) technique will be introduced as a useful and versatile tool for nano-fluidics. We illustrate it with two specific examples involving nano-pores as building blocks for nano-fluidics. Nano-pores, either biological, solid-state, or ultra thin pierced grapheme, are powerful tools which are central to many applications, from sensing of biological molecules to desalination and fabrication of ion selective membranes. [Preview Abstract] |
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F1.00068: Study of surface charge density on solid/liquid interfaces by modulating the electrical double layer Hyuk Kyu Pak, Jong Kyun Moon A solid surface in contact with water or aqueous solution usually carries specific electric charges. These surface charges attract counter ions from the liquid side. Since the geometry of opposite charge distribution parallel to the solid/liquid interface is similar to that of a capacitor, it is called an electrical double layer capacitor (EDLC). Therefore, there is an electrical potential difference across an EDLC in equilibrium. When a liquid bridge is formed between two conducting plates, the system behaves as two serially connected EDLCs. In this work, we propose a new method for investigating the surface charge density on solid/liquid interfaces. By mechanically modulating the electrical double layers and simultaneously applying a DC bias voltage across the plates, an AC electric current can be generated. By measuring the voltage difference between the plates as a function of bias voltage, we can study the surface charge density on solid/liquid interfaces. Our experimental results agree very well with the simple equivalent circuit model proposed here. Furthermore, using this method, one can determine the polarity of the adsorbed state on the solid surface depending on the material used. [Preview Abstract] |
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F1.00069: Investigation and visualization of flow through porous media at the pore scale Sophie Roman, Cyprien Soulaine, Anthony Kovscek In this work, a micro-Particle Image Velocimetry (micro-PIV) system is used to quantitatively investigate the dynamics of fluid displacement in simplified porous media. The porous media under study are 2D etched micromodels containing a flow pattern either composed of circular grains homogeneously distributed or made of a sandstone replica pattern. The fluid is seeded with microparticles which are used to estimate the velocity field with PIV algorithms. The exact pore-scale velocity profiles are obtained in the case of a fully saturated porous medium with a typical pore size of 5-40$\mu$m. The experimental velocity measurements are compared with 2D direct numerical simulations of the flow through the two different geometries under consideration. We have shown that the micro-PIV measurements have produced results in very good agreement with the numerical simulations for single-phase flows. Therefore, this experimental technique can be used with confidence to investigate flow properties in porous media. In particular this technique can be powerful for the study of immiscible two-phase flow in porous media in a wide range of parameters, for which numerical tools are still in development and need reliable data to be validated. [Preview Abstract] |
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F1.00070: COMPLEX FLOWS AND COMPLEX FLUIDS |
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F1.00071: ABSTRACT WITHDRAWN |
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F1.00072: Enhancement of Sublimation of Single Graphene Layer by Interacting with Gas Molecules in Rarefied Environment Ramki Murugesan, Jae Hyun Park Graphene has excellent mechanical properties. One of them is the resistance to high temperature environment. Since the sublimation temperature of graphene is over 4500 K, it has been used for diverse high temperature applications in order to protect the system. In this study, using extensive molecular dynamics simulations, we show that the sublimation of graphene could be enhanced (occurs at the lower temperature) by interacting with the gas molecules. With increase in temperature, the bonds in graphene becomes so sensitive to interact with the incoming gas molecules. When the temperature is low, the graphene is stable to the impingement of gas molecules: The light H$_2$ gases are stick to the graphene surface and remains being attached while the heavy CO$_2$ and H$_2$O are bounced back from the surface. However, at high temperature H$_2$ gases are absorbed on the graphene and destroy the C$-$C bonds by forming C$-$H bonds. The local breakage of bond at the impingement spot spreads the entire graphene soon, causing a complete sublimation. Even though the heavy CO$_2$ and H$_2$O molecules also break the C$-$C bonds at high temperature,but their impingement effect is localized and the breakage does not propagate over the entire surface. [Preview Abstract] |
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F1.00073: Characteristics of contaminant deposition onto a cylindrical body surrounded by porous clothing Minki Cho, Jinwon Lee, Hyunsuk Jung, Haewan Lee In order to characterize the deposition pattern of air-borne contaminants on a human body protected by a garment, the air flow through the clothing and in the air gap between the clothing and the skin was numerically solved, and the deposition of the suspended contaminants on the skin was obtained over a wide variety of conditions-wind speed, human motion and clothing conditions. The penetrating air flow was sensitive to the pressure inside the air gap, for which a simple model was successfully formulated. Also the profile of the non-uniform deposition velocity or the Sherwood number could be well modeled based on the developing concentration boundary layer inside the air gap. The boundary layer thickness grew vary rapidly, nearly proportional to the square of the distance from the front stagnation point, which is much different from any other boundary layer studied in many engineering fields before. A rather universal function for the distribution of deposition speed over a cylindrical body was obtained, which remained valid for a very wide range of conditions. The characteristics for non-uniform and/or periodic external wind due to human motion were also analyzed. [Preview Abstract] |
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F1.00074: Stability of viscoelastic wakes Luca Biancofiore, Luca Brandt, Tamer Zaki Theoretical and computational studies of synthetic wakes have explained the dynamics of several industrial and technological flows, for example mixing in fuel injection and papermaking, and the flow behind bluff bodies. Despite the industrial importance of complex non-Newtonian flow, previous work has focused on Newtonian fluids. Nonlinear simulations of viscoelastic, spatially-developing wakes are performed in order to analyze the influence of polymer additives on the behavior of the flow. Viscoelasticity is modeled using the FENE-P closure. A canonical wake profile (Monkewitz, Phys. Fluids, 88) is prescribed as an inflow condition, and the downstream evolution is computed using the full Navier-Stokes equations for a range of Reynolds and Weissenberg numbers. The simulations demonstrate that the influence of the polymer can be stabilizing or destabilizing, depending on the inlet velocity profile. Smooth profiles are stabilized by elasticity while sharp profiles are destabilized. The disturbance kinetic energy budget is examined in order to explain the difference in behavior and in particular the influence of the polymeric stresses on flow stability. [Preview Abstract] |
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F1.00075: Mass flow rate of granular material in silos with lateral exit holes Abraham Medina, Armando Serrano, Florencio Sanchez In this work we have analyzed experimentally the mass flow rate, m', of the lateral outflow of cohesionless granular material through circular orifices of diameter D and rectangular and triangular slots of hydraulic diameter D$_{\mathrm{H}}$ made in vertical walls of bins. Experiments were made in order to determine also the influence of the wall thickness of the bin, w. Geometrical and physical arguments, are given to get a general correlation for m' embracing both quantities, D (D$_{\mathrm{H}})$ and w. The angle of repose is also an important factor characterizing these flows. [Preview Abstract] |
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F1.00076: A continuum approach to study reversible shear thickening fluid behavior Hua-Yi Hsu In this work we explore if it is possible to reproduce reversible shear thickening behavior by using continuum equations. A critical shear stress indicates the transition of reversible shear thickening. To the end it is noted that reversible shear thickening fluid behavior is affected by (i) Hydrodynamic force (ii) Brownian motion, and (iii) Electrostatic force. To incorporate the features, we simulate shearing flow between two walls in the presence of external potential source term. The shear- stress-versus-viscosity trend is similar to the experimental results. At low shear stress range, the viscosity decreases as the stress increases. After reaching the critical shear stress, the viscosity increases as the stress increases. An understanding of the overall force balance and the critical shear stress emerges from the governing equations. [Preview Abstract] |
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F1.00077: Shock wave mitigation using Newtonian and non-Newtonian fluids Xingtian Tao, Brendan Colvert, Veronica Eliasson The effectiveness of a wall of liquid as a blast mitigation device is examined using a shock tube and a custom-designed and -built shock test chamber. High-speed schlieren photography and high-frequency pressure sensors allow measurement during the relevant shock interaction time periods of the liquid-gas interface. The characteristic quantities that reflect these effects include reflected-to-incident shock strength ratio, transmitted-to-incident shock strength ratio, transmitted and reflected impulse, and peak pressure reduction. In particular, the effects of viscous properties of the fluid are considered when using non-Newtonian dilatant and pseudoplastic fluids. Experiments have been performed with both Newtonian and non-Newtonian fluids. The impact of a shock waves on Non-newtonian fluids is compared to that of Newtonian fluids. Experiments show that non-Newtonian fluids have very strong reflection properties, acting like solid walls under the impact of a shock wave. Further work is to be performed to compare quantitatively the properties of Newtonian vs. non-Newtonian fluids. [Preview Abstract] |
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F1.00078: EXPERIMENTAL FLUID MECHANICS |
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F1.00079: Lift Force Acting on Bodies in Viscous Liquid Under Vibration Vitaliy Schipitsyn, Alevtina Ivanova, Olga Vlasova, Victor Kozlov The averaged lift force acting on a rigid body located near the wall of the cavity with a viscous liquid under high-frequency oscillations of various types is studied experimentally and theoretically. The experiments are conducted with cylindrical and rectangular solids. Amplitude and frequency of vibration, viscosity and density of fluid, specific solid size, its density and shape vary. Lift force was measured by the dynamic hanging of the body in the gravity when the body oscillates without touching the cavity walls. The vibrations generate a repulsive force, holding a heavy body above the bottom of the cavity, and the light one at some distance from the ceiling. Lift force changes qualitatively in case of combined translational and rotational oscillations of the cavity containing fluid and solid; it is much greater than at the translational vibrations and appears throughout the entire volume of the liquid. The work contains a theoretical description of the mechanism of lift force generation and the comparison of the experimental and theoretical results. The agreement of the results is found in the limit of high dimensionless frequencies. The considered effects could be interesting for vibrational control of solid inclusions in viscous liquids. [Preview Abstract] |
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F1.00080: Experiments and models of particle slurries Katherine Varela, Sarah Burnett, Andrew Li, Matthew Molinare, Dirk Peschka, Jeffrey Wong, Andrea Bertozzi We present new experimental and theoretical results for the resuspension of bidisperse particle-laden flows on an inclined plane. In particular, we study the case of two negatively buoyant particle species of similar size and dissimilar densities in a viscous fluid of finite volume. Different regimes of particle separation are observed and studied by adjusting the angle of inclination, total particle concentration, and relative particle volume ratio. In addition to obtaining information about the height profile of shock formations, we measure the advancement and separation of particle and fluid front positions in mono- and bidisperse scenarios. These dynamics are the basis for a quantitative understanding of polydisperse cases, which can be readily applied to industry and catastrophe modeling. [Preview Abstract] |
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F1.00081: Experimental Study of Spanwise Wake Compression of a Trapezoidal Pitching Panel Justin King, Zachary Berger, Melissa Green Stereoscopic particle image velocimetry was used to characterize the highly three-dimensional flow created by a rigid, trapezoidal pitching panel used to model an idealized fish caudal fin. Previous work has demonstrated that spanwise compression of the wake occurs until the wake ultimately breaks down as it convects in the streamwise direction. However, quantitative verification of the spanwise velocity relevant to the structure of this compression was not evaluated in the prior work. Experiments were conducted over a range of Strouhal numbers from 0.17 to 0.56 at three locations along the spanwise extent of the wake. Ongoing stereo PIV measurements confirm spanwise flow in the wake toward the midspan, which agrees with the previously-observed linear spanwise compression as the wake moved downstream. [Preview Abstract] |
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F1.00082: Study of interfaces in an Axisymmetric Supersonic Jet using Background Oriented Schlieren (BOS) Carlos Echeverr\'Ia, David Porta, Alejandro Aguayo, Hiroki Cardoso, Catalina Stern We have used several techniques to study a small axisymmetric supersonic jet: Rayleigh scattering, Schlieren Toepler and PIV. Each technique gives different kind of information. In this paper, a BOS set-up is used to study the structure of the shock pattern. A shadowgraph of a dot matrix is obtained with and without a flow. The displacement field of the dots is related to changes in the index of refraction, which can be related, through the Gladstone-Dale equation, to changes in density. Previous results with this technique were not conclusive because of the relative size of the dots compared to the diameter of the nozzle. Measurements have been taken for three different exit speeds. [Preview Abstract] |
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F1.00083: Calibration of a Background Oriented Schlieren (BOS) Set-up David Porta, Carlos Echeverr\'ia, Hiroki Cardoso, Alejandro Aguayo, Catalina Stern We use two materials with different known indexes of refraction to calibrate a Background Oriented Schlieren (BOS) experimental set-up, and to validate the Lorenz-Lorentz equation. BOS is used in our experiments to determine local changes of density in the shock pattern of an axisymmetric supersonic air jet. It is important to validate, in particular, the Gladstone Dale approximation (index of refraction close to one) in our experimental conditions and determine the uncertainty of our density measurements. In some cases, the index of refraction of the material is well known, but in others the density is measured and related to the displacement field. [Preview Abstract] |
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F1.00084: Rise of aqueous foam in vertical pipes Valeriano \'Alvarez, Andr\'es Perez, Ignacio Carvajal, Florencio S\'anchez, Abraham Medina In this work we made many experiments on aqueous foams formation, the generation is done through a constant flow of gas from the bottom of the tube, by means of a capillary, we observed two cases, the first case was with the top tube open to the atmosphere and the second case is the same tube now covered. We measure vertical profiles of the foam rise velocities. These velocities are affected by properties of the foam solution and the interaction with the material tube as the surfactant type, angle contact, the type of foam generator, and different diameter of the pipe. [Preview Abstract] |
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