Bulletin of the American Physical Society
2006 59th Annual Meeting of the APS Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2006; Tampa Bay, Florida
Session FE: Multiphase and Particle-Laden Flows II |
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Chair: Nicholas Taberlet, DAMPT, University of Cambridge Room: Tampa Marriott Waterside Hotel and Marina Florida Salon 123 |
Monday, November 20, 2006 8:00AM - 8:13AM |
FE.00001: Behavior of Shock Solutions in Particle-Laden Thin Films Bejamin Cook, Andrea Bertozzi, A.E. Hosoi We study a suspension of heavy particles in an advancing film of viscous liquid. Particle settling in the normal and in-plane directions occurs, and is dependent on the angle of the plane with respect to gravity. At steep angles, settling in the normal direction appears insignificant, and in-plane settling leads to the formation of a packed ridge at the contact line. A lubrication-type model of this phenomenon featuring concentration-dependent viscosity and settling rates takes the form of a 2x2 hyperbolic system of conservation laws, with double-shock solutions qualitatively matching these observations. However the Richardson-Zaki hindered settling function leads to a loss of hyperbolicity near the maximum concentration, and sometimes an insoluble Riemann problem. We suggest a modified hinderance function that vanishes at the maximum packing fraction and eliminates these concerns. We also consider rarefaction solutions for the constant volume case and compare these with Huppert's well-known single-rarefaction solution for a clear fluid. [Preview Abstract] |
Monday, November 20, 2006 8:13AM - 8:26AM |
FE.00002: Investigation of Unsteady Forces on a Particle in a Compressible Flow M. Parmar, A. Haselbacher, S. Balachandar The acceleration of a body immersed in a fluid gives rise to so-called added-mass and history forces because some of the surrounding fluid is accelerated due to no-penetration condition and due to the developent of the boundary layer. These forces have been studied in detail, both theoretically and numerically, for incompressible flows and spherical particles. The purpose of the present investigation is to assess the effect of compressibility on these forces. Our primary interest is in strong accelerations of particles such as by impacting shock waves. To this end, we have modified an existing unstructured-grid fluids code to solve the Navier-Stokes equations in a moving frame of reference. The acceleration of the moving frame is determined from the instantaneous force on the particle and its mass. To improve the accuracy of the computations, non-reflecting boundary conditions are used at the outer boundary. Preliminary results in two dimensions will be presented for several acceleration rates. [Preview Abstract] |
Monday, November 20, 2006 8:26AM - 8:39AM |
FE.00003: Numerical Investigation of Filtration by Circular and Elliptical Fibers Jing Wang, David Pui Numerical simulation has been carried out to investigate filtration by circular and elliptical fibers. The flow field through arrays of fibers and the drag force on individual fibers are obtained. The simulation results are in good agreement with analytical solutions for the drag on circular and elliptical fibers obtained from the cell model. Our simulation covers mechanisms for particle capture due to interception, inertial impaction and diffusion. The efficiency due to interception and inertial impaction are obtained by determining the critical initial position, below which all the particles are captured. Particle capture due to diffusion is studied by solving the convective diffusion equation for the particle concentration. The simulation results for particle capture are converted into single-fiber efficiencies and compared to theoretical expressions in the literature, which are limited to circular fibers; reasonable agreement is obtained. We extend the calculation for the single-fiber efficiencies to different elliptical fibers. The figure of merit, which is defined as the ratio of the collection efficiency to the pressure drop, is computed for different elliptical fibers. It is found that the figure of merit depends on the particles under consideration. Blunt and close to circular fibers are more effective for particles dominated by the effects of interception and inertial impaction, whereas long and slim fibers are more effective for particles dominated by the diffusion effect. [Preview Abstract] |
Monday, November 20, 2006 8:39AM - 8:52AM |
FE.00004: Effect of Drag Reducing Polymers on Stratified and Stratified/Annular Flow in a Horizontal Duct Patricia Pernica, Brian Fleck, Ted Heidrick An investigation was carried out to determine the effects of a drag reducing additive (DRA) on two phase flow in horizontal stratified and stratified/annular flow patterns. Experiments were conducted in an air-water flow in a transparent rectangular channel of cross-section 25.4 mm $\times $ 50.8 mm and 2.5 m in length. Pressure drop measurements, wave characteristics and observations of entrainment with and without DRA are presented. A non-contact measurement technique using laser induced fluorescence and high speed videography was used to measure span-wise liquid wave heights and to characterize the air-water interface. Pressure drop was measured at the centerline of the duct over a one meter distance. The onset of entrainment was observed visually. Effects of DRA were observed even at a low concentration of 5ppm. This concentration yielded pressure drop reductions of 10-15{\%} which correlate with previous experiments done in horizontal pipelines.\footnote{Al-Sarkhi, A., Hanratty, T.J., Int J. Multiphase Flow, \underline {27}, 1151 (2001)} Observations also show dampening of roll waves and the suppression of atomization. [Preview Abstract] |
Monday, November 20, 2006 8:52AM - 9:05AM |
FE.00005: Spin Coating of a Colloidal Suspension Yongli Zhao, Jeffrey Marshall A computational model is presented that utilizes a thin-film finite-difference code together with a discrete-element method for colloidal particles to simulate the transport, collision and adhesion of small particles in a liquid film during a spin coating process. Both van der Waals adhesion and capillary forces on the particles at the gas-liquid interface are considered. Spin coating processes are of particular interest for formation of nanoparticle films, where a controlled concentration distribution of nanoparticles in the final film is desired. The computational model is used to examine the effect of particle collisional forces on particle dispersion in the film during spin coating, as well as aggregate formation and particle adhesion to the substrate surface, as functions of the ratio of particle size to film thickness, the adhesion parameter, the particle concentration, and the Rossby number of the spin coating process. [Preview Abstract] |
Monday, November 20, 2006 9:05AM - 9:18AM |
FE.00006: Dynamic three-dimensional simulations of densely-packed fluid loaded cloth in a complex geometry Deniz T. Akcabay, William W. Schultz, David R. Dowling This talk presents three-dimensional simulations of the fluid-structure interaction that occurs inside the washtub of a modern clothes washing machine. The results are based on the numerical solution of the incompressible Navier-Stokes equations on a Cartesian grid using Peskin's Immersed Boundary Method for the cloth-fluid coupling, and a weighted domain-mapping method to represent the complicated moving boundaries of the agitator and washtub. Cloth pieces are modeled as impermeable flexible isotropic elastic plates. Results from simple benchmarking studies with theoretical and experimental results for the individual cloth and complex geometry models are presented. A variety of simulation studies involving complicated mixing patterns that result from mechanical excitation from a realistic agitator are shown and analyzed. The effects of cloth size, bending stiffness, and load density on the resulting motion of individual pieces of cloth and on the bulk flow within the machine are analyzed. [Sponsored by Whirlpool Corporation] [Preview Abstract] |
Monday, November 20, 2006 9:18AM - 9:31AM |
FE.00007: Shock-Wave Diffraction at a Right-Angled Corner in a Particle-Laden Gas A. Haselbacher, F. Najjar, S. Balachandar Many explosions can be abstracted as a strong shock wave moving into the atmosphere, followed by a contact discontinuity which separates the post-shock conditions from a particle- or fragment-laden region. The interaction of the shock wave itself and the flow behind the shock wave with obstacles creates complex flow patterns. The diffraction of a shock wave at a right-angled corner in a particle-laden gas can be viewed as a simple representation of the interaction with an obstacle. We have studied this configuration numerically using an unstructured-grid compressible-flow code with high-resolution spatial-discretization methods and Lagrangian tracking for the particles. The primary focus of the study is to quantify the effect of the particles on the various flow features encontered behind the shock front, such as the contact discontinuity, secondary and tertiary shocks, and the vortex. [Preview Abstract] |
Monday, November 20, 2006 9:31AM - 9:44AM |
FE.00008: High Speed Time Resolved Stereo PIV Measurements of Particle Laden Jets in Crossflows F.J. Diez, P. Alvare, P.B. Vanderwerker, S. Pothos, D. Troolin The velocity properties of steady round particle laden jets were studied, motivated by applications to the dispersion of potentially harmful substances from steady exhaust flows, volcanic eruptions, hydrothermal plumes, among others. In order to elucidate the mechanism of particle dispersion, simultaneous recording of particle dispersion and turbulent structures in three-dimensional space is required. For this purpose, a novel high speed time resolved 3D PIV imaging measurement system was developed. The system is capable of tracking the 3D velocity field of both the dispersed phase (large solid particles or air bubbles) and the smaller particle tracers in jets in crossflow at 2,000 Hz. This method also allows for the first time in particle-laden experiments to get the entire field of view in directly in three-dimension, and time-resolved instantaneous velocity fields which will allow the visualization of the evolution of the 3D turbulent coherent structures as a function of time as well as the evolution of the dispersed phase. The difficulty in evaluating simultaneous two-phase PIV images comes when trying to separate the dispersed phase from the neutrally buoyant small solid tracers in the water. The present work uses the phase discrimination method proposed by Khalitov {\&} Longmire (2002) due to its robustness and flexibility while also being relatively cheap to implement. [Preview Abstract] |
Monday, November 20, 2006 9:44AM - 9:57AM |
FE.00009: Particle Aggregation and Deposition in a Micro-nozzle Flow John Mousel, Jeffrey Marshall A discrete-element model for adhesive particulate flows is applied to study particle transport in a micro-nozzle flows. A soft-sphere particle collision model, modified for adhesive forces, is combined with a level-set method to efficiently transport the particles on a Cartesian mesh. Of particular interest is examination of the ability of van der Waals force to cause particle to adhere to the nozzle wall and to each other, forming aggregates both freely transported by the nozzle flow and attached to the nozzle wall. The study examines the physical processes by which particle aggregates attached to the wall interact with those transported by the flow. The percentage of particles captured by the nozzle walls is evaluated as a function of adhesion parameter, particle size, particle concentration, and nozzle contraction ratio and contraction rate. Of particular interest are conditions leading to formation of a particle bridge blocking the nozzle. [Preview Abstract] |
Monday, November 20, 2006 9:57AM - 10:10AM |
FE.00010: Pseudo-turbulence intensity in mono-dispersed bubbly liquids R. Zenit, J. Martinez-Mercado, C.A. Palacios-Morales Experiments were performed to measure the mean and fluctuating velocities of both phases in a bubbly flow in a vertical column. Using water and water-glycerin mixtures, measurements were obtained for a range of Reynolds numbers from 10 to 500, corresponding to Weber numbers smaller than 2. A carefully designed bubble generator and the addition of a small amount of salt, produced a nearly mono-dispersed bubble size. Measurements of the bubble phase velocity were obtained using a dual impedance probe and through high speed digital video processing. A measurement of the fluctuating component of the liquid velocity was obtained using of a \emph{flying} hotfilm technique. It was found that, for all cases, the mean bubble velocity decreases as mean gas volume fraction increases. The flow agitation, characterized by the velocity variance, both in the liquid and the bubble phases, increases with bubble concentration. Surprisingly, the pseudo-turbulent intensities are found to increase as the Reynolds number decreases. Direct comparisons with recent theoretical and computational studies for the same range of conditions will be presented. [Preview Abstract] |
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