Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session MV: Suspenions I |
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Chair: Dewei Qi, Western Michigan University Room: Ballroom B |
Tuesday, November 25, 2008 8:00AM - 8:13AM |
MV.00001: On the anisotropic thermal conductivity of magnetorheological suspensions Jerry Shan, Benjamin Reinecke, Karl Subedissen, Anna Cherkasova The thermal conductivity of an iron-based magnetorheological suspension is experimentally investigated and found to be enhanced, anisotropic, and hysteric under magnetic fields due to the formation of field-induced chains. The component of the thermal conductivity in the field direction more than doubles under the applied field in some instances, while the conductivity remains essentially unchanged in the directions perpendicular to the field. Hysteresis is found in which the effective conductivity, once enhanced by the field, remains high until the fluid is disturbed to break the particle chains. A two-level homogenization model for both components of the effective thermal-conductivity tensor is developed and compared with the data. The structural implications of the model are discussed in relation to theoretical predictions of the microstructure of the saturated suspension. [Preview Abstract] |
Tuesday, November 25, 2008 8:13AM - 8:26AM |
MV.00002: Segregation and mixing in bidisperse liquid-fluidized suspension Ang\'elique Deboeuf, Georges Gauthier, J\'er\^ome Martin, Dominique Salin We study experimentally the fluidization of a bidisperse suspension of macroscopic particles (100 to 160 microns for the smallest beads and 180-200 microns for the largest glass beads), at low Reynolds number. With the help of an acoustic scanner, the measurement of the sound propagation (velocity and attenuation), is continuously recorded along the bed. Those measurements are linked to the concentrations of the particles, and provide the composition, in time, of the suspension along the vertical axis. In our system, one may expect a segregation process induced by the different settling velocities, which should result in a stationary segregated state: a monodisperse suspension of small particles fluidized on top of a monodisperse suspension of large particles, with a transition zone enlarged by the mixing of particles due to hydrodydamic dispersion. However, for some concentration and ratio of beads diameter, no stationary state has been observed in our experimental system: our fluidized bidisperse suspension exhibits oscillations between segregated and homogeneous states. [Preview Abstract] |
Tuesday, November 25, 2008 8:26AM - 8:39AM |
MV.00003: Liquid flow through particulate systems: from foam drainage to the settling of semi-dilute suspension Florence Rouyer, Olivier Pitois, Nicolas Louvet, Elise Lorenceau We show that the model of permeability proposed by Kozeny and Carman and originally validated on packed beds of spheres -- with porosity around 0.4 -- is a particular case and can be extented to liquid fraction from 0.001 up to 0.85 for systems made of monodisperse entities. The knowledge of the specific surface area is essential. This modeling allow us to well describe experimental results from drainage of aqueous dry foam up to sedimentation of semi-dilute suspension. [Preview Abstract] |
Tuesday, November 25, 2008 8:39AM - 8:52AM |
MV.00004: Simulation of suspension flow of finite-size spherical particles in a 3D square channel Hui Gao, Lian-Ping Wang Suspension flow of finite-size particles in a turbulent gas is of importance to many engineering applications and natural phenomena. As a first step, the present work focuses on the motion and hydrodynamic interaction of finite-size particles in the absence of background carrier-fluid turbulence. The major challenge for an accurate simulation is twofold: an efficient implementation of no-slip boundary conditions on the moving particle surface and an accurate representation of short-range lubrication effects that typically are not resolved numerically. A Navier-Stokes based hybrid approach (i.e., Physalis) developed by Prosperetti and co-workers is employed to solve the suspension flows of a pair of finite-size, freely-moving particles at finite particle Reynolds numbers. A lubrication force representation, designed by Ladd, involving particle relative location and velocity, is incorporated to capture the short-range interactions between particles. The accuracy of the representation and its compatibility with the flow simulation will be examined. A mesoscopic lattice Boltzmann equation (LBE) approach is also used to simulate the same problem for cross validation. Specific implementation issues will be addressed. Comparison with available numerical data will also be discussed. [Preview Abstract] |
Tuesday, November 25, 2008 8:52AM - 9:05AM |
MV.00005: Nonlinear dynamics of ordered particle arrays in parallel-wall channels under creeping-flow conditions Jerzy Blawzdziewicz, Eligiusz Wajnryb, Nidhi Khurana We investigate wave propagation and structural transitions in flow-driven or force-driven particle arrays confined in parallel-wall channels. Our numerical simulations reveal that square and hexagonal particle arrays tend to maintain ordered structure, which is stable with respect to relatively large perturbations. Evolution of such perturbations can be described in terms of a superposition of propagating displacement waves. We show that coupling between longitudinal and transverse waves may lead to lattice instabilities. Under some conditions there occurs a rapid transition from an ordered square lattice to partially ordered hexagonal structure with a large number of defects. This new nonequilibrium fluctuating structure resembles 2D hexatic equilibrium phase. [Preview Abstract] |
Tuesday, November 25, 2008 9:05AM - 9:18AM |
MV.00006: Steerable filters as a tool to determine the orientation of fibers in flowing suspensions Allan Carlsson, Fredrik Lundell, L. Daniel S\"oderberg Fiber suspension flows are found in industrial applications such as paper manufacturing and polymer processing. In order to experimentally study fiber motions in such suspensions it is essential to be able to determine the position and orientation of fibers as a function of time. One method to extract this information from captured images is to use image filtering. The image filtering is based on computing convolutions of the images with a filter matrix that resembles a fiber. Steerable filters represent a class of filters where an arbitrary orientation of the filter can be obtained from a linear combination of a limited set of basis filters. Since the basis filters are not orientation dependent this makes it possible to eliminate the orientation dependency from the convolutions. Here a specific steerable filter is evaluated for functionality of finding the position and orientation of fibers in a flowing suspension. Through application of the filter on artificially generated test images with known fiber orientation it is possible to show that the error is less than 1 degree. A good agreement is also found when comparing the orientation distribution with a robust, but computationally more expensive, method on a real flow case where fibers are suspended in a shear flow. [Preview Abstract] |
Tuesday, November 25, 2008 9:18AM - 9:31AM |
MV.00007: Instabilities in the dynamics of neutrally buoyant particles Themistoklis Sapsis, George Haller The asymptotic dynamics of finite-size particles is governed by a slow manifold that is globally attracting for sufficiently small Stokes numbers. For neutrally buoyant particles (suspensions), the slow dynamics coincide with that of infinitesimally small particles, therefore the suspension dynamics should synchronize with Lagrangian particle motions. Paradoxically, recent studies observe a scattering of suspension dynamics along Lagrangian particle motions. Here we resolve this paradox by proving that despite its global attractivity, the slow manifold has domains that repel nearby passing trajectories. We derive an explicit analytic expression for these unstable domains; we also obtain a necessary condition for the global attractivity of the slow manifold. Additionally, we show that the results are extended for the non-neutrally buoyant particles case. We illustrate our theoretical findings on inertial particle motion in a two-dimensional model of vortex shedding behind a cylinder in crossflow, on the three-dimensional steady Arnold-Beltrami-Childress flow, as well as to the realistic flow field of a hurricane. [Preview Abstract] |
Tuesday, November 25, 2008 9:31AM - 9:44AM |
MV.00008: Pattern Formation in a Rotating Suspension of Non-Brownian Buoyant Particles Bruce Ackerson, Makrand Kalyankar, W.R. Matson, Penger Tong This study examines concentration and velocity patterns observed in a horizontal rotating cylinder completely filled with a monodisperse suspension of non-Brownian buoyant particles. The unique patterns or phases are mapped by varying both the rotation rate and the solvent viscosity. Individual phases are identified using both frontal ($\theta$-$z$ plane) and axial ($r$-$\theta$ plane) views. Phase boundaries are compared to those obtained recently for suspensions of non- buoyant particles. Expressing the boundaries in terms of dimensionless parameters unifies the data for several samples at low rotation rates. When centrifugal force dominates, the behavior becomes quite different from previous studies. [Preview Abstract] |
Tuesday, November 25, 2008 9:44AM - 9:57AM |
MV.00009: Terminal velocity and velocity fluctuations of sedimenting suspensions in quasi 2D geometry Rodrigo Soto, Alejandra Alvarez, Francisco Mena Buoyant suspensions, confined in a quasi two-dimensional geometry, are studied using the Hele-shaw model. In the far field regime, boundary integral methods allow to compute the pressure field and the resulting hydrodynamic interactions. The result is a self-consistent set of equations that include the effect of particle correlations, the effective medium and container walls. Interactions are long-ranged, with effective forces decaying as $R^{-2}$, leading to undefined values for the terminal velocity. A regularization scheme, modeling the counterflow due to the presence of limiting walls in the sedimentation direction, is derived. The resulting regularized model leads to finite terminal velocity and fluctuations that do not depend on the system size nor its shape. [Preview Abstract] |
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