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 BQ: Particle Laden Flows I |
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Chair: Xiaolong Yin, Colorado School of Mines Room: 202B |
Sunday, November 23, 2008 10:30AM - 10:43AM |
BQ.00001: Particle Segregation in the Presence of Oscillating Straining Flows Jeffrey Marshall Numerical experiments performed using a discrete-element method for both adhesive and non-adhesive particles have demonstrated that particles placed in an oscillating straining flow will drift toward the nodal points of straining -- a phenomenon that we refer to as \textit{oscillatory clustering}. A theory explaining this phenomenon is proposed and used to predict the particle drift rate, which is found to increase with increase in particle Stokes number up to a stability limit. The theory also predicts that in the presence of gravitational force, particles will exhibit a limit cycle behavior in which they oscillate under the opposing downward gravitational drift and upward drift due to oscillatory clustering. Computations are performed to demonstrate the effects of this phenomenon for particles in an oscillating box, for peristaltic pumping of a particulate suspension, and for a suspension flowing through a corrugated tube. [Preview Abstract] |
Sunday, November 23, 2008 10:43AM - 10:56AM |
BQ.00002: The Effect of Particles on the Dissipation of Dissipation Coefficient in the k-$\varepsilon $ Model John Schwarzkopf, Clayton Crowe, James Riley, Prashanta Dutta A volume average k-$\varepsilon $ model for particle laden flows is presented. Recently a turbulent dissipation transport equation was derived to support the TKE equation developed by Crowe and Gillant (1998). To obtain the dissipation model, the coefficients were assumed to be related to those associated with the single phase model yet include effects of the dispersed phase. An analysis shows that four non-dimensional parameters are inherent in modeling particle laden flows: 1) Fluid Reynolds number (Re), 2) Particle Reynolds number (Re$_{p})$, 3) Particle mass concentration (C), and 4) Stokes number (St). Direct numerical simulation was used to isolate the effect of stationary particles in homogeneous turbulent decay at low Reynolds numbers (Re = 3.3 and 12.5). The particles were positioned at each grid point and modeled as point forces and a comparison was made between a 64$^{3}$ and 128$^{3}$ domain. The results show that the dissipation of dissipation coefficient correlates well with the ratio of particle mass concentration to Stokes number (C/St). [Preview Abstract] |
Sunday, November 23, 2008 10:56AM - 11:09AM |
BQ.00003: Particle Tracking for Membranes Including Filtration Darryl James, Stephen Webb Particle transport including filtration is an important phenomenon in many engineering and biological systems. Phenomenological modeling of a cross-flow filtration experiment has been performed to investigate the biofouling potential of a porous membrane. Spherical particles sized one micron and smaller are released into a steady flow field. The porous membrane is characterized by a Darcy number equal to 10$^{8}$. Forces include electric double layer (EDL), van der Waals (vdW), induced lift, and transverse and Stokes-corrected normal drag including near-wall effects. For the negatively charged particles investigated, the EDL and vdW forces become significant within only within one particle radius from the membrane and produce repulsive and attractive forces respectively. Results will be presented quantifying fouling performance as a function of particle sizes, and cross-flow and filtration velocities and compared with experimental data. [Preview Abstract] |
Sunday, November 23, 2008 11:09AM - 11:22AM |
BQ.00004: Effect of ambient flow inhomogeneity on forces on a finite-sized particle Jungwoo Kim, S. Balachandar In particle-laden flows involving particle transport and dispersion, the prediction of forces acting on the particle in a nonuniform flow is one of the central issues. However, existing analytical expressions and empirical correlations have been mostly developed for uniform or other simple linear ambient flows. Therefore, in this study we perform direct numerical simulations of a finite-sized spherical particle in a cellular flow field in order to improve knowledge concerning the influence of the spatial flow-variations on the forces acting on the particle in more general flows. To do so, the ratio of the particle diameter (D) and the cell size in the cellular flow (L) is varied in the range of $0.01 \leq {\rm D}/ {\rm L} \leq 0.2$. In this study, the instantaneous drag force is separately considered as quasi-steady and unsteady components. Then, each force component is compared with existing expressions for the corresponding force on the particle. The present study shows that in the presence of the spatial variations, the effect of flow inhomogeneity on the quasi-steady drag appear to be larger than what is predicted by the Faxen correction derived in creeping flow. These results are used in our understanding of forces on a finite-sized particle in turbulent flows. [Preview Abstract] |
Sunday, November 23, 2008 11:22AM - 11:35AM |
BQ.00005: Particle self-diffusion in a viscous shear flow: from hydrodynamic interactions to collisional effects Micheline Abbas, Eric Climent, Olivier Simonin, Martin Maxey Particle shear-induced self-diffusion is investigated at low Reynolds and variable Stokes $St$ numbers. We simulated the suspension hydrodynamics for $St<<1$ by using the Force Coupling Method. For suspensions with finite particle inertia (finite $St$), we proposed a new Eulerian prediction based on the kinetic theory for granular flows which has been validated by discrete particle simulations assuming Stokes drag and binary collisions (for low to moderate solid concentration). On the microscopic level, the particle velocity fluctuations have a Gaussian distribution shape for both high and vanishing $St$, whereas they show a highly peaked distribution for suspensions characterized by $St~O(1)$ and low solid volume fractions. On the macroscopic level, the self-diffusion tensor is strongly anisotropic and the diffusive behavior becomes more prominent when the particle inertia increases. The self-diffusion coefficients decrease with concentration at high $St$. The results will be analyzed in terms of analogies and differences between the two regimes investigated (hydrodynamic interactions or collisional effects). [Preview Abstract] |
Sunday, November 23, 2008 11:35AM - 11:48AM |
BQ.00006: Simulation and Modeling of Explosive Dispersal of Compressed Gas-Particle Suspensions Yue Ling, Andreas Haselbacher, S. Balachandar Some effects of a detonating particle-laden explosive can be modeled through the explosion of a compressed gas-particle suspension. The suspension can be considered to be located in a spherical container and released through the instantaneous removal of the container similar to a shock tube. The transient flow generated by the removal of the container is well understood in the case without particles. Comparatively little is known about the dispersal of the particles and the unsteady interactions between the various waves and the particles. The objective of this work is to use Eulerian-Lagrangian simulations to improve our understanding of the dispersal of particles. Particular attention is focused on the interactions of the particles with the expansion fan and their effect on the flow behavior at large times. Parametric studies are carried out to systematically investigate the effects of particle size, particle density, and mass fraction. [Preview Abstract] |
Sunday, November 23, 2008 11:48AM - 12:01PM |
BQ.00007: DNS of fully resolved spherical particles dispersed in isotropic turbulence Francesco Lucci, Antonino Ferrante, Said Elghobashi Our DNS study concerns the interactions between decaying isotropic turbulence and solid spherical particles with diameter, $d$, larger than the Kolmogorov length scale, $\eta$. We employ an Immersed Boundary method similar to that of Uhlmann (JCP, 2005) to resolve the flow around $6400$ spherical particles with a volume fraction of $\phi_v=0.1$. The monosize particles have a diameter, $d = 16 \eta_o$. Our simulations, with $256^3$ mesh points and $Re_{\lambda_0} = 75$, cover a range of $38 \le \tau_p/\tau_{K_o} \le 149$, for the ratio of the particle response time to the initial Kolmogorov time scale. A Lagrangian approach is used to compute the frequency spectrum of the turbulence kinetic energy (TKE) of the fluid phase. The effects of varying $\tau_p/\tau_{K_o}$ on the spectrum and the decay rate of TKE are discussed. The effects of the formation of the particle boundary layer on the viscous dissipation rate of TKE are also discussed. [Preview Abstract] |
Sunday, November 23, 2008 12:01PM - 12:14PM |
BQ.00008: Phase portrait of irreversible low-Reynolds number flow Guandong Zhu, Marina Popova, Marc Ingber, Peter Vorobieff We present a computational and experimental study of a two-dimensional shear flow carrying spherical particles. While the Reynolds number characterizing the problem is very small, dissipative interactions between the particles lead to irreversibility and apparent chaos. We use experimental results as the starting point for a numerical simulation of such irreversible interactions within a three-particle system, investigating its phase space by introducing subtle changes to the initial positions of the particles. Our simulation uses traction-corrected boundary element method (TC-BEM) and reveals a surprisingly rich behavior in good agreement with experiment. [Preview Abstract] |
Sunday, November 23, 2008 12:14PM - 12:27PM |
BQ.00009: A variable-density fictitious-domain method for fully resolved simulation of high-density ratio fluid-particle systems Sourabh Apte A numerical scheme for fully resolved simulation of fluid-particle systems with freely moving rigid particles is developed. The approach is based on a fictitious domain method wherein the entire fluid-particle domain is assumed to be a fluid and the flow inside the particle domain is constrained to be a rigid body motion using an additional rigidity constraint in a three-stage fractional step scheme. The particle is assumed to be made up of material points moving on a fixed background mesh where the fluid flow equations are solved. The basic finite-volume solver is based on a co-located grid incompressible, but variable-density, flow. The incompressibility constraint is imposed by solving a variable-coefficient pressure equation giving rise to a stable scheme for high density ratio fluid-particle systems. This scheme is used to simulate a range of single and multiple particle problems in laminar flows. Application of the scheme for the simulation of large number of fully resolved particles in wall-bounded turbulent flows, such as those occur in sediment transport, will be discussed. [Preview Abstract] |
Sunday, November 23, 2008 12:27PM - 12:40PM |
BQ.00010: A Two Fluid Algorithm for Incompressible Flows Laden with Low Stokes Number Particles Babak Shotorban For small Stokes numbers the particle velocity can be expressed in terms of the velocity and acceleration of the carrier phase through a series expansion [Maxey, JFM, 1987]. Consequently, the back-way coupling effect of particles on the carrier phase can be accounted for only in its momentum equation through modifying its density via a two fluid approach. The modified density is a function of the particle volume fraction. A new algorithm is proposed to solve this momentum equation for an incompressible carrier phase based on the projection method of Chorin, Math. Comp. 1968. Some benchmark problems are solved to test the new algorithm. [Preview Abstract] |
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