Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session H31: Particle Laden Flows IV |
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Chair: Said Elghobashi, University of California, Irvine Room: 33B |
Monday, November 19, 2012 10:30AM - 10:43AM |
H31.00001: Near-surface sea spray dynamics via simulations of particle-laden, turbulent Couette flow David Richter, Peter Sullivan In the atmospheric surface layer situated over the air-sea interface, high winds can eject large amounts of sea spray into the turbulent flow above. The question of whether or not this dispersed phase within the turbulent surface layer can alter momentum transfer from the air to the ocean surface remains unresolved. This study, therefore, aims to identify and explain modifications of wall-normal momentum transfer in a turbulent, particle-laden flow. This is done using direct numerical simulation (DNS) with a Lagrangian point-particle representation of the dispersed phase. Turbulent Couette flow, chosen since it exhibits certain features similar to the atmospheric surface layer, is investigated with varying concentrations and sizes of spherical, non-interacting particles. Generally speaking, the addition of a dispersed phase disrupts the motions responsible for turbulent, carrier-phase momentum transfer, while at the same time compensating for this loss of momentum transfer through an additional dispersed phase stress. Mechanisms and interpretations of these changes in turbulent wall-normal momentum transport will be presented. [Preview Abstract] |
Monday, November 19, 2012 10:43AM - 10:56AM |
H31.00002: Numerical study of the boundary conditions in particulate suspensions with the lattice Boltzmann method Lina Xu, Laura Schaefer Particulate suspensions are common phenomena in industrial and biological fields. However, the fundamental understanding of the hydrodynamic interactions between the solid and fluid needs to be further improved. The lattice Boltzmann method has been shown to be an effective numerical method to model various fluid flows, and exhibits good performance in dealing with boundary conditions, with straightforward and easy-to-implement methods for complex solid boundaries. In this presentation, the units transfer between the lattice Boltzmann system and the physical system is characterized in detail, in order to simulate flows from the realistic physical world. Force evaluations, based on the momentum exchange method and the FH model used to implement boundary conditions, are shown for both a static and moving cylinder in a 2D channel. Finally, the settling trajectory of the cylinder after it is released away from the centerline in a Poiseuille flow is investigated with varying Reynolds numbers. [Preview Abstract] |
Monday, November 19, 2012 10:56AM - 11:09AM |
H31.00003: DNS of particle dispersion in a spatially developing turbulent boundary layer Michael Dodd, Keegan Webster, Antonino Ferrante We performed DNS of particle-laden spatially developing turbulent boundary layer at Re$_\theta=1000-3200$. We computed the Lagrangian trajectories of millions of fluid points and solid particles of three different Stokes number, St=0.1, 1, and 5. The particles were gradually released from a line source. We computed the time development of particle mean displacement, dispersion, and turbulent diffusivity. Our DNS results of fluid point mean-displacements are in excellent agreement with those of Batchelor's (1964) theory. Also, our DNS results show that in general particle statistics are strongly influenced by particle's Stokes number. Such dependence is mostly caused by the particles tendency to preferentially accumulate in the viscous sublayer as their Stokes number increases. Furthermore, for $t/T_L<1$ where $T_L$ is the Lagrangian integral time scale, the streamwise and wall-normal dispersions are $\propto t^{2}$ for fluid points and $\propto t^{3}$ for solid particles. For $20 |
Monday, November 19, 2012 11:09AM - 11:22AM |
H31.00004: Modeling near-wall interphase exchanges for particle-laden flows Olivier Desjardins, Jesse Capecelatro In Eulerian-Lagrangian and Eulerian-Eulerian modeling approaches of dispersed multiphase flows, proper treatment of mass and momentum transfer between the phases is required to capture the correct physical behavior. Coupling often involves the volume fraction and momentum exchange term based on correlations for drag. The accuracy of these terms diminishes at regions close to walls, where key assumptions that were used in the formulation of the models are often violated. Defining particle volume fraction close to a solid boundary could require using detailed information on the distance between the surface of the particles and the wall. No-slip boundary conditions are imposed on the fluid phase while particles may slip, complicating the momentum transfer. In addition, experiments have reported enhanced lift at the walls, corresponding to values greater than what can be estimated from Saffman shear-induced models. In this study, coupling between the phases is handled in an Euler-Lagrange framework using a two-step filtering process that ensures a conservative exchange, as well as convergence under mesh refinement. A turbulent spout fluidized bed is simulated, and compared to experimental data. Different strategies are explored to properly account for the presence of the walls. [Preview Abstract] |
Monday, November 19, 2012 11:22AM - 11:35AM |
H31.00005: Particle equilibrium in 3D-channel flow for one and two particles Joy Klinkenberg, H.C. de Lange, Wim-Paul Breugem, Luca Brandt We perform Direct Numerical Simulations of an Euler-Lagrange coupled particle-laden channel flow to investigate the equilibrium position of particles. The channel is periodic in both stream- and spanwise direction, with no-slip on top and bottom walls. Particles are neutrally buoyant and modeled using the Immersed Boundary Method, with a dimater of 20{\%} of the channel height. The lateral movement of one and two particles is studied for Reynolds numbers, based on channel height and bulk velocity, between 5 and 1000. We show that with a Reynolds number change, the equilibrium position changes. To investigate the effect of periodicity, several channel lengths and widths have been investigated. Also the effect of particle-particle interaction on the equilibrium is investigated by modelling 2 particles, influencing each other. [Preview Abstract] |
Monday, November 19, 2012 11:35AM - 11:48AM |
H31.00006: Particle Dynamics in Rotating Flow inside Coaxial Cylinder Albert S. Kim, Sungsu Lee In this study, trajectory and distribution of unequal-sized particles in a coaxial cylinder are investigated using dissipative hydrodynamics (DHD), an updated version of Stokesian dynamics. Flow field is established by rotating an inner cylinder in a fixed outer cylinder. Initially, particles are randomly released in the flow. The flow field is then decomposed into unidirectional flow, vortice and rate-of-strain at particle centers. Translation and rotation of particles are accurately mimicked using the fourth-rank hydrodynamic tensors. In general, far-field many-body grand mobility matrix was formed at each time step as a function of particle positions, and inverted to calculate the grand resistance matrix. The Langevin equation is directly solved to trace the particle trajectory using the intermediate time step to physically mimic influence of force and torque. Particle inertia is intrinsically included as rotational fluid speed increases from the surface of the inner cylinder to that of the outer cylinder. Optimal operation conditions to separate particles due to size differences are suggested by DHD simulation results. This work was financially supported by projects of the ''Development of Energy utilization technology with Deep Ocean Water,'' KIOST of Korea. [Preview Abstract] |
Monday, November 19, 2012 11:48AM - 12:01PM |
H31.00007: Numerical studies of the effects of neutrally buoyant large particles on turbulent channel flow at the friction Reynolds number up to 395 Zhaosheng Yu, Yu Wang, Xueming Shao A direct-forcing fictitious domain method was employed to perform fully-resolved numerical simulations of turbulent channel flow laden with large neutrally buoyant particles at constant pressure gradients. The effects of the particles on the turbulence (including the fluid-phase average velocity, the root-mean-square (rms) of the velocity fluctuation, the probability density function of the velocity and the vortex structures) at the friction Reynolds number of 180 and 395 were investigated. The results show that the drag-reduction effect caused by the spherical particle at low particle volumes is very small. The presence of particles decreases the maximum rms of streamwise velocity fluctuation near wall via weakening the large-scale streamwise vortices, and on the other hand increases the rms of transverse and spanwise fluctuating velocities in vicinity of the wall via inducing smaller-scale vortices. The effects of the particles on the fluid velocity PDF (probability density function) normalized with the rms velocity are small, irrespective of the particle size, particle volume fraction and Reynolds number. [Preview Abstract] |
Monday, November 19, 2012 12:01PM - 12:14PM |
H31.00008: Four-way coupling simulation of particle-laden turbulent channel flow Junghoon Lee, Changhoon Lee Transport of small inertial particles near a wall in turbulent flows is frequently observed in various engineering applications. In this kind of flow, the gas-phase turbulence level may be modified due to the presence of the particles. Furthermore, for sufficiently high volume fractions, particle-particle interactions strongly influence particle dispersion and thus four-way coupling becomes essential in simulation of particle-laden turbulence. In this study, we investigate inertial particle motion in near-wall turbulence using direct numerical simulations. The effects of inter-particle collisions and particle feedback on the fluid were taken into account in our spectral simulation. It is assumed that inertial particle motion is governed by Stokes drag, lift and gravitationa forces. Particle deposion, velocity and acceleration statistics are discussed for various Stokes numbers and particle volume fractions. The particle Stokes number is defined as the particle response time normalized by the wall units. The Stokes number range considered is 25$\sim$2,000 and particle volume fraction ranges from $3 \times 10^{-6}$ to $ 6 \times 10^{-5}$. We also compare our numerical results with available experimental measurements. Detailed results will be presented in the meeting. [Preview Abstract] |
Monday, November 19, 2012 12:14PM - 12:27PM |
H31.00009: Behavior of particles in turbulence over a wavy wall Hea Eun Lee, Changhoon Lee Particle motion in near-wall turbulence plays an important role in many physical processes such as sediment transport and pollution control. There have been many studies which focused on particles in turbulence over a flat wall. Behavior of particles over a rough wall, however, was not investigated much. In this study, particle motion in turbulent flow over a wavy wall is investigated using direct numerical simulation. The wave-induced variation of flow is simulated by spectral method and compared with the flow over a flat wall. The virtual boundary method proposed by Goldstein et al. (1995) is applied to impose no-slip condition at wavy boundary. To begin with, we focused on the differences between turbulence generated at a wavy boundary and one at a flat wall such as friction factors, velocity fluctuations, and vortical structures associated with shear layers that form behind the wave. Also, focusing on the mechanism controlling the inertial particles in turbulence, particle motion in turbulence over wavy wall is investigated. Due to the turbulent structure modified by wavy geometry, inertial particles are clustering in upslope part of the wall which is the region with high shear stress. Detailed particle statistics over a wavy wall will be discussed in the meeting. [Preview Abstract] |
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