Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session GV: Particle Laden Flows: Simulations II |
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Chair: Eckart Meiburg, University of California, Santa Barbara Room: Hyatt Regency Long Beach Regency B |
Monday, November 22, 2010 8:00AM - 8:13AM |
GV.00001: Renormalized transport of inertial particles Marco Martins Afonso, Antonio Celani, Andrea Mazzino, Piero Olla We study how an imposed flow (laminar or turbulent) modifies the transport properties of inertial particles, namely their terminal velocity and effective diffusivity. Such quantities are investigated by means of analytical and numerical computations, as functions of the control parameters of both flow and particle; i.e., density ratio, inertia, Brownian diffusivity, gravity (or other external forces), turbulence intensity, compressibility degree, space dimension, and geometric/temporal properties. The complex interplay between these parameters leads to the following conclusion of interest in the realm of applications: any attempt to model sedimentation processes (or, equivalently, floater transport by surface winds) cannot avoid taking into account the full details of the flow field and of the inertial particles. [Preview Abstract] |
Monday, November 22, 2010 8:13AM - 8:26AM |
GV.00002: Particulate Flow over a Backward Facing Step Preceding a Filter Medium Frank Chambers, Krishna Ravi Computational Fluid Dynamic predictions were performed for particulate flows over a backward facing step with and without a filter downstream. The carrier phase was air and the monodisperse particles were dust with diameters of 1 to 50 microns. The step expansion ratio was 2:1, and the filter was located at 4.25 and 6.75 step heights downstream. Computations were performed for Reynolds numbers of 6550 and 10000. The carrier phase turbulence was modeled using the k-epsilon RNG model. The particles were modeled using a discrete phase model and particle dispersion was modeled using stochastic tracking. The filter was modeled as a porous medium, and the porous jump boundary condition was used. The particle boundary condition applied at the walls was ``reflect'' and at the filter was ``trap.'' The presence of the porous medium showed a profound effect on the recirculation zone length, velocity profiles, and particle trajectories. The velocity profiles were compared to experiments. As particle size increased, the number of particles entering the recirculation zone decreased. The filter at the farther downstream location promoted more particles becoming trapped in the recirculation zone. [Preview Abstract] |
Monday, November 22, 2010 8:26AM - 8:39AM |
GV.00003: ABSTRACT WITHDRAWN |
Monday, November 22, 2010 8:39AM - 8:52AM |
GV.00004: Numerical simulation of particle laden coaxial turbulent jet flows Kumaran Kannaiyan, Reza Sadr The study of coaxial turbulent particle laden jets has been of interest due to its importance in many applications such as industrial burners, and mixing devices. The addition of the second phase to the continuous phase jet can change the already complicated flow pattern and turbulent characteristics of the jets. Albeit the vast research efforts that have been devoted to understand such phenomena, demand for detailed investigation of particle laden flows remains an active area of research. The advent of laser diagnostics has helped to quantify the myriad details of the jet flow fields in more details. In parallel computational fluid dynamics (CFD) can provide additional information by further investigating such flows with an acceptable level of accuracy. In this work, numerical simulations results are presented for the flow and turbulent characteristics of a coaxial jet with and without the dispersed phase. The results are compared with the experimental data measured using Molecular Tagging Velocimetry diagnostic technique. The key objective of this work is to undermine the flow field details that are difficult if not impossible to measure. [Preview Abstract] |
Monday, November 22, 2010 8:52AM - 9:05AM |
GV.00005: A-priori reconstruction of ideal stochastic forcing for particle motion in turbulent flow Maria Vittoria Salvetti, Sergio Chibbaro, Federico Bianco, Cristian Marchioli, Alfredo Soldati One issue associated with the use of Large-Eddy Simulation (LES) to study the dispersion of small inertial particles in turbulent flow is the accuracy with which particle statistics and concentration can be reproduced. The motion of particles in LES fields may differ significantly from that observed in experiments or Direct Numerical Simulation (DNS) because the force acting on particles is not well estimated when only the filtered fluid velocity is available, and because errors accumulate in time leading to progressive trajectories divergence. We identify herein an Ideal Forcing (IF) such that trajectories of individual particles moving in a-priori LES fields in turbulent channel flow coincide with particle trajectories in a DNS. The objective is to compute PDF and statistical moments of IF to possibly identify a stochastic process from which IF could be extracted and then used as closure model for the particle motion equations. [Preview Abstract] |
Monday, November 22, 2010 9:05AM - 9:18AM |
GV.00006: Eulerian-Lagrangian Simulations of Three-Dimensional Turbulent Riser Flows Jesse Capecelatro, Perrine Pepiot, Olivier Desjardins Particle suspended flows in vertical risers are used in many industries in the form of circulating fluidized beds. Applications include gasification/pyrolysis for biofuel conversion, coal combustion, and fluid catalytic cracking. Experimental studies have shown riser flows to be unsteady with large particle concentration fluctuations. Regions of densely packed particles, referred to as clusters form, which greatly affect the overall flow behavior and mixing properties. Because the solid phase is opaque, quantitative experimental results are limited, and therefore computational fluid dynamics (CFD) is used here to simulate 3D riser flows. The gas phase is solved with a high-order fully conservative finite difference code called NGA, tailored for turbulent flow computation. Lagrangian tracking is used to solve the particle phase. Statistics are computed for both the gas and particle phases, along with characteristic cluster sizes, shape, and velocities. Inter-particle collisions are considered and shown to affect the clustering behavior of the flow. [Preview Abstract] |
Monday, November 22, 2010 9:18AM - 9:31AM |
GV.00007: Numerical prediction of pollutant dispersion into ABL; a Lagrangian approach using LES Michael Morikone, Stefan Llewellyn Smith, Marcel Ilie Air pollution is one of the major environmental challenges facing humankind today. The accurate prediction of fate and transport of pollutants into the atmospheric boundary layer would improve the health quality and duration of human life, and thus is of critical importance. The pollutants are transported along the wind direction, but it is the atmospheric turbulence that determines the dispersion of the pollutants. An efficient Eulerian-Lagrangian particle dispersion algorithm for the prediction of pollutant dispersion in the atmospheric boundary layer (ABL) is proposed. The volume fraction of the dispersed phase is assumed to be small enough such that particle-particle collisions are negligible and properties of the carrier flow are not modified. With the examination of dilute systems only the effect of turbulence on particle motion has to be taken into account (one-way coupling). With this assumption the continuous phase can be treated separate from the particulate phase. The continuous phase is determined by large-eddy simulation in the Eulerian frame of reference whereas the dispersed phase is simulated in a Lagrangian frame of reference. The results of the present study indicate that the particle shape and size influences the particle dispersion. [Preview Abstract] |
Monday, November 22, 2010 9:31AM - 9:44AM |
GV.00008: Coherent vortex interaction with a particle-laden boundary layer Fernando Morales, Iftekhar Naqavi, Kyle Squires, Ugo Piomelli The focus of the current investigations is numerical modeling of particle entrainment in turbulent boundary layers with and without coherent vortices superimposed on the background flow. Simulations are performed using an Euler-Lagrange method in which a fractional-step approach is used for the fluid and with the particulate phase advanced using Discrete Particle Simulation. The first flow field models a rotor wake comprised of gradually introduced coherent vortices into a turbulent boundary layer. The second flow is a turbulent boundary layer without vortices to discriminate and characterize the effect of the vortex structures on the dispersed phase properties. The third case models interaction of a coherent vortex introduced into a stagnant bed of particles. The simulations are performed with two groups of particles having different densities both of which display strong vortex-particle interaction close to the source location, and with mixing of the particles into the boundary layer downstream. Visualizations and statistical descriptors quantify the strong effect of the coherent vortex structures on dispersed phase properties. [Preview Abstract] |
Monday, November 22, 2010 9:44AM - 9:57AM |
GV.00009: Large-eddy simulation of turbulent collision of heavy particles in isotropic turbulence Guodong Jin, Guowei He The small-scale motions relevant to the collision of heavy particles represent a challenge to LES of turbulent particle-laden flows. We examine the capability of the LES method to predict the collision-related statistics such as the collision rate for a wide range of particle Stokes numbers. It is shown that, without the SGS motions, LES cannot accurately predict the particle-pair statistics for heavy particles with small and intermediate Stokes numbers. The errors from the filtering operation and the SGS model are evaluated separately using the filtered-DNS (FDNS) and LES flow fields. The errors increase with the filter width and have nonmonotonic variations with the particle Stokes numbers. It is concluded that the error due to filtering dominates the overall error in LES for most particle Stokes numbers. It is found that a particle SGS model must include the effects of SGS motions on the turbulent collision of heavy particles for $St_k < 3$. For more details please refer to Phys. Fluids 22, 055106 (2010). [Preview Abstract] |
Monday, November 22, 2010 9:57AM - 10:10AM |
GV.00010: Effects of Inter-Particle Collisions and Two-Way Coupling on Particle Deposition Velocity in a Turbulent Channel Flow Hojjat Nasr, Goodarz Ahmadi, John McLaughlin This study was concerned with the effect of particle-particle collisions and two-way coupling on the particle deposition velocity in a turbulent channel flow. The time history of the instantaneous turbulent velocity vector was generated by the two-way coupled direct numerical simulation (DNS) of the Navier-Stokes equation via a pseudospectral method. The particle equation of motion included the Stokes drag, the Saffman lift, and the gravitational forces. The effect of particles on the flow was included in the analysis via a feedback force that acted on the fluid on the computational grid points. Several simulations for different particle relaxation times and particle mass loading were performed, and the effects of the inter-particle collisions and two-way coupling on the particle deposition velocity, fluid and particle fluctuating velocities, particle normal mean velocity, and particle concentration were determined. It was found that when particle-particle collisions were included in the computation, the particle deposition velocity increased. When the particle collision was neglected but the particle-fluid two-way coupling was accounted for, the particle deposition velocity decreased slightly. For the four-way coupling case, when both inter-particle collisions and two-way coupling effects were taken into account, the particle deposition velocity increased. Comparisons of the present simulation results with the available experimental data and earlier numerical results are also presented. [Preview Abstract] |
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