Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session BP: Particle-Laden Flows II |
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Chair: S. Elghobashi, University of California, Irvine Room: Salt Palace Convention Center 251 D |
Sunday, November 18, 2007 10:34AM - 10:47AM |
BP.00001: Modeling particle deposition in a turbulent ribbed channel flow Amirul Khan, Xiaoyu Luo, Franck Nicolleau, Paul Tucker, Giovanni Lo Iacono Transport and deposition of aerosol particles in a plane channel with a ribbed wall are studied to investigate the effects of turbulent flow structures on particle deposition. In this paper, kinematic simulation (KS) has been adapted to be a sub-grid model for particles, in conjunction with large eddy simulation (LES) simulation in real space. KS is a Lagrangian model of turbulent dispersion that takes into account the effects of spatio-temporal flow structure on particle dispersion. It is a unified Lagrangian model of one-, two- and indeed multi-particle turbulent dispersion and can easily be used as a Lagrangian sub-grid model for LES code thus enabling complex geometry to be taken into account. To study the effect of small scale flow structures on particle deposition in the ribbed channel flow we use a validated LES code to simulate the flow field, and KS to model the sub-grid flow structures. Comparing our results with published experimental data suggest that the particle deposition in the ribbed channel can be greatly affected by the small-scale (sub-grid) turbulent flow structures. [Preview Abstract] |
Sunday, November 18, 2007 10:47AM - 11:00AM |
BP.00002: Sediment deposition from bouyant river plumes Lutz Lesshafft, Eckart Meiburg, Ben Kneller The ground deposition patterns of sediments that are carried by a river into the ocean are studied via numerical simulation. The bouyant plume of particle-laden fresh water evolving in ambient sea water near the estuary is assumed to spread axisymmetrically. Model predictions, both for the flow field and for the sediment deposition, are derived from the shallow water approximation as well as from the boundary layer equations. Predictive capabilities of these models are assessed by comparison to results from direct numerical simulations. [Preview Abstract] |
Sunday, November 18, 2007 11:00AM - 11:13AM |
BP.00003: Near-bed sediment transport by coherent structures in the turbulent flow past a surface-mounted cylinder. Cristian Escauriaza, Fotis Sotiropoulos Fluctuations on the instantaneous hydrodynamic forces produced by coherent structures are responsible for the initiation of motion and transport of sediment particles in turbulent flows. The bed-load transport near the threshold of motion driven by these unsteady vortical structures is characterized by intermittent displacement events of varying magnitudes with particles saltating or sliding on the bed. In this study, we utilize a hybrid URANS/LES turbulence model to capture the large-scale coherent structures in the turbulent flow around a vertical cylinder mounted in a rectangular channel. We develop a Lagrangian model to carry out one-way coupling simulations of inertial particles near the bed and investigate the transport process by performing a detailed statistical analysis of the sediment flux. The quantitative description of the sediment dynamics will provide insights on the fundamental mechanisms of particle entrainment and transport, and clarify the role of the coherent structures in determining the time-scales of sediment motion for realistic flow conditions. [Preview Abstract] |
Sunday, November 18, 2007 11:13AM - 11:26AM |
BP.00004: The behavior of the temperature of small inertial particles in turbulent flow Saensuk Wetchagarun, James Riley Heat transfer between phases plays a crucial role in many multiphase flow problems, e.g., in multiphase combustion systems. We report on a study of heat transfer to/from small inertial particles in a turbulent flow using direct numerical simulation with computational grids up to 512$^3$ grid points. The ambient fluid is subject to a uniform mean temperature gradient; the particle concentration is assumed to be dilute, so that one-way coupling is assumed in both the momentum and the energy equations. Inertial particles for a range of Stokes and Nusselt numbers are considered. In addition, both ensemble-averaged statistics as well as subgrid-scale statistics are computed, and both Eulerian and particle-tracking reference frames are utilized. Considering subgrid-scale modeling, this analysis is used, e.g., for the $\textit{a priori}$ testing of models for the subgrid-scale Eulerian velocity and temperature fields as experienced by the inertial particles. In addition, the relationship between the fluid particle temperature statistics and the fluid particle velocity is explored, as well as the relationship between the inertial particle temperature statistics and the autocorrelation of the Eulerian temperature field experienced by the particle. [Preview Abstract] |
Sunday, November 18, 2007 11:26AM - 11:39AM |
BP.00005: Flow Modification and Heat Transfer Enhancement Using Ferromagnetic Particle Laden Fluid with Switched Magnetic Fields Mark Murray A convective heat transfer enhancement technique and the experimental methods used to quantify the improvement in heat transfer and subsequent differential pressure rise are introduced. The enhancement technique employs time varying magnetic fields produced in a pipe to cause the ferromagnetic particles of a particle laden fluid to be attracted to and released from the pipe wall. The ferromagnetic particles act not only to advect heat into the bulk fluid, but they also significantly modify the flow field disrupting the boundary layer, allowing cooler fluid to reach the high temperature pipe wall, increase thermal energy transfer directly to the fluid and contribute to the overall improvement in heat transfer rate. The enhancement technique demonstrated a 250{\%} increases in heat transfer coefficient with only a corresponding 48{\%} increase in flow differential pressure for the experimental parameters tested. It is also found that magnetic field switching frequency significantly influences both enhancement and pressure drop magnitudes. [Preview Abstract] |
Sunday, November 18, 2007 11:39AM - 11:52AM |
BP.00006: Fully resolved DNS of freely moving finite-size particles in decaying isotropic turbulence Said Elghobashi, Antonino Ferrante The objective of the present study is to investigate the two-way coupling effects of freely moving {\em finite-size} solid particles on decaying isotropic turbulence. The particle diameter is of the order of the Taylor micro- scale of turbulence, $\lambda$, i.e. $d\sim\lambda > \eta$, and the volume fraction of particles $\phi_v\sim 0.1$. Our DNS employs an {\em immersed boundary method} to resolve the flow around each individual particle while simultaneously resolving the fluid motion at the Kolmogorov scale. The Navier-Stokes equations are solved throughout the whole domain (including the volumes occupied by the particles) on a Cartesian mesh. The number of the dispersed particles is $88$ for $ \phi_v=0.01$, and $884$ for $\phi_v=0.1$. The density of the solid particles is 2.56 times that of the carrier fluid. The modifications of the decay rate and the spectrum of the turbulence kinetic energy and its dissipation rate are discussed. [Preview Abstract] |
Sunday, November 18, 2007 11:52AM - 12:05PM |
BP.00007: Self-consistent calculation of a spherical particle's motion in a tangle of superfluid vortices Demosthenes Kivotides, S. Louise Wilkin In thermal superfluid turbulence\footnote{D. Kivotides, Phys. Rev. Lett. {\bf 96}, 175301 (2006)}, a superfluid component interacts via mutual friction forces with a normal-fluid component. At present, there are no experimental methods for the direct measurement of the local normal-fluid velocity in such systems. Recently, experimentalists\footnote{T. Zhang and S. W. Van Sciver, Nature Phys. {\bf 1}, 36 (2005)}$^,$\footnote{G. P. Bewley {\it et al},Nature {\bf 44}, 588 (2006)} introduced micron-sized particles in thermal superfluids and measured (using Particle Image Velocimetry) their velocity. What is the relation between the measured particle velocity and the superfluid or normal-fluid velocities? Since superfluid turbulence is characterized by complex tangles of nanometer core size vortices that appear as ideal line vortices at the scale of the particles and reconnect with the latter, the answer to this question is not straightforward. In response to these matters, we have recently developed methods\footnote{D. Kivotides {\it et al}, J. Low Temp. Phys. {\bf 144}, 121 (2006)} for the self-consistent computation of vortex-particle interactions that treat successfully reconnections. We report results of such calculations that, by corresponding directly to superfluid turbulence experiments, provide clues for their understanding. [Preview Abstract] |
Sunday, November 18, 2007 12:05PM - 12:18PM |
BP.00008: Characteristics of drag and lift forces of a finite-sized particle in isotropic turbulence Jungwoo Kim, S. Balachandar In the problem of particle-laden flows, the prediction of drag and lift forces acting on the particle in the presence of turbulence is one of the most important issues. In order to investigate the effect of turbulence at the level of a single particle, we perform direct numerical simulations of an isolated particle subjected to free-stream turbulence, following Bagchi \& Balachandar (2003). The particle Reynolds number ranges from 100 to 350. At each particle Reynolds number, the turbulent intensity is about 5-20 percent of the mean relative particle velocity and the corresponding diameter of the particle is comparable to or larger than the Kolmogorov scale. In this study, the instantaneous force is decomposed into the drag and lift forces. Then, the statistical characteristics of the forces are investigated. The present result shows that the use of the stationary sphere drag as quasi-steady force improves the estimation of the drag force as compared to the Schiller-Neumann drag correlation. In addition, the modification of wake dynamics due to turbulence and its relation to the forces acting on the particle is presented. We also investigate the case of a freely moving particle and explore its effect. [Preview Abstract] |
Sunday, November 18, 2007 12:18PM - 12:31PM |
BP.00009: Experiemetal study of turbulent transport of material particles Mickael Bourgoin, Nauman Qureshi, Unai Arrieta, Christophe Baudet, Alain Cartellier, Yves Gagne We report measurements of Lagrangian velocity and acceleration statistics of particles transported in a turbulent flow obtained with an acoustic Doppler velocimetry technique. We consider a homogeneous isotropic grid turbulence generated in a wind tunnel with a Reynolds number based on Taylor microscale of R $\sim$ 180. We focus on the effects of particles finite size and of the particle to fluid density ratio. The versatility of our setup allows to explore a parameter space over a significant range of particles densities and sizes. An intermittent dynamics, with time scale dependent statistics of Lagrangian velocity increments, is observed for all particles size and density, though intermittency has different signature depending on particles density. Acceleration probability density function is found non-gaussian and independent on particles size and density. In particular acceleration statistics are not found to tend to gaussian as the particles Stokes number increases. Though the global shape of acceleration statistics does not change, the acceleration variance does strongly depend on particles size and density. Systematic trends will be discussed. [Preview Abstract] |
Sunday, November 18, 2007 12:31PM - 12:44PM |
BP.00010: Simulation of Bubble-Vortex Interaction by the Eulerian-Lagrangian Approach Ehsan Shams, Sourabh Apte We perform simulations of bubble dynamics in vortex-dominated flows, such as a line vortex, using the Eulerian-Lagrangian approach. The motion of large number of bubbles is simulated by assuming spherical, point-particles with models for added mass effects, drag, and lift forces. The bubble growth/collapse is modeled by the Rayleigh-Plesset (RP) equation using Runge-Kutta scheme with adaptive time-stepping to accurately capture the bubble dynamics. Three modeling approaches are considered: (a) one-way coupling; where the influence of the bubble on the fluid flow is neglected, (b) two-way coupling; where the momentum exchange between the fluid and the bubbles is modeled, and (c) finite-volume bubbles; where the volumetric displacement of the fluid by the bubble motion and the momentum-exchange are modeled. The bubbles spiral around the vortex and are eventually captured in the central core. The effect of bubbles on the vortex as predicted by the two-way coupling models will be discussed for both constant and time-varying bubble sizes. [Preview Abstract] |
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