Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session MK: Particle Laden Flows III |
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Chair: Steve Ceccio, University of Michigan Room: 101J |
Tuesday, November 24, 2009 8:00AM - 8:13AM |
MK.00001: Analysis of dense particulate flow dynamics using a Euler-Lagrange approach Olivier Desjardins, Perrine Pepiot Thermochemical conversion of biomass to biofuels relies heavily on dense particulate flows to enhance heat and mass transfers. While CFD tools can provide very valuable insights on reactor design and optimization, accurate simulations of these flows remain extremely challenging due to the complex coupling between the gas and solid phases. In this work, Lagrangian particle tracking has been implemented in the arbitrarily high order parallel LES/DNS code NGA [Desjardins et al., JCP, 2008]. Collisions are handled using a soft-sphere model, while a combined least squares/mollification approach is adopted to accurately transfer data between the Lagrangian particles and the Eulerian gas phase mesh, regardless of the particle diameter to mesh size ratio. The energy conservation properties of the numerical scheme are assessed and a detailed statistical analysis of the dynamics of a periodic fluidized bed with a uniform velocity inlet is conducted. [Preview Abstract] |
Tuesday, November 24, 2009 8:13AM - 8:26AM |
MK.00002: Rheology, Microstructure and Migration in Brownian Colloidal Suspensions Wenxiao Pan, Bruce Caswell, George Karniadakis We demonstrate that suspended spherical colloidal particles can be effectively modelled as single dissipative particle dynamics (DPD) particles provided that the conservative repulsive force is appropriately chosen. The suspension model is further improved with a new formulation, which augments standard DPD with non-central dissipative shear forces between particles while preserving angular momentum. Using the new DPD formulation we investigate the rheology, microstructure and shear-induced migration of a monodisperse suspension of colloidal particles in plane shear flows (Couette and Poiseuille). Our simulations yield relative viscosity versus volume fraction predictions in good agreement with both experimental data and empirical correlations. We also compute the shear-dependent viscosity and the first and second normal- stress differences and coefficients in both Couette and Poiseuille flow. Simulations near the close packing volume- fraction (64\%) at low shear rates demonstrate a transition to flow-induced string-like structures of colloidal particles simultaneously with a transition to a non-linear Couette velocity profile. Migration effects simulated in Poiseuille flow compare well with experiments and model predictions. Overall, the new method agrees very well with the Stokesian Dynamics method but it seems to have lower computational complexity and is applicable to general complex fluids systems. [Preview Abstract] |
Tuesday, November 24, 2009 8:26AM - 8:39AM |
MK.00003: Discrete Element Modeling of Particle Transport by an Electric Curtain Jeffrey Marshall, Guanqing Liu Particle transport by a planar electric curtain is studied with a discrete element method (DEM). The electric curtain is consists of four sets of parallel stripe electrodes embedded in an insulating material. The electrodes are connected to a four-phase square-wave AC source and produce a traveling wave above the curtain plate. Current work focuses on different modes of particle transport and associated operating conditions, which include particle relevant properties (size, charge, adhesive surface energy, air drag) and device relevant parameters (amplitude, frequency of applied AC voltage). Both Coulomb and dielectrophoretic forces on particles are considered. The electric field produced by the curtain is solved by a two-dimensional boundary element method (BEM). The computation is validated by comparison with experimental data for particle transport speed. A series of simulations are conducted to investigate the influence of different factors, demonstrating different modes of particle transport. The effect of air flow over the curtain on transport of levitated particles is examined. The particle motion is found to exhibit a wealth of interesting phenomena due to the complex and combined affects of different physical parameters and processes. [Preview Abstract] |
Tuesday, November 24, 2009 8:39AM - 8:52AM |
MK.00004: Modeling Visco-elastic Particle Collision in Coupled Direct Numerical/Discrete Particle Simulations Julian Simeonov, Joseph Calantoni We study particle collision with coupled Direct Numerical Simulations (DNS) and Discrete Particle Simulations (DPS) where the flow and the particle evolution are determined from the Navier-Stokes and Newton's equations of motion, respectively. The hydrodynamic force on a particle is obtained by integrating the resolved pressure and viscous stress on the particle surface, and the normal and tangential particle- contact forces are modeled with springs and friction. Resolving visco-elastic collisions in DNS/DPS requires integrating the fluid equations at time steps of a few microseconds that are prohibitively small for modeling large turbulent systems. We develop a robust collision scheme for coupled DNS/DPS where the fluid integration time step is much larger than the particle time step. The scheme is based on two- particle DNS/DPS with matching fluid and particle time steps. The visco-elastic restitution coefficient obtained in the two-particle simulations and its dependence on the collisional Stokes number is compared to experimental results. [Preview Abstract] |
Tuesday, November 24, 2009 8:52AM - 9:05AM |
MK.00005: Coarse grid simulation of dense fluidized bed: a dynamic subgrid drag model Jean-Francois Parmentier, Olivier Simonin, Olivier Delsart Unresolved structures in 3D unsteady simulation of gas-particle fluidized bed using the two-fluid model approach can have a drastic influence on the flow dynamic. In particular, dense fluidized bed expansion may be widely overestimated. Such an effect can be inputed to the coarse modeling of the resolved drag term in the momentum equations. Filtered two-fluid model formalism highlights the need to account for a drift velocity due to the subgrid correlation between the fluid velocity and particle concentration fields. A priori analysis were performed from highly resolved simulations of dense fluidized beds. Results gathered provide us constitutive relationship to close this drift velocity and we proposed a dynamic model to predict the filtered drag force. This model was a-posteriori tested on ``coarse-grid'' fluidized bed simulations. Simulation results compared fairly well to fully resolved simulations and experimental bed expansions. [Preview Abstract] |
Tuesday, November 24, 2009 9:05AM - 9:18AM |
MK.00006: Partitioning of particle temperature in gas-solid turbulent flows Enrica Masi, Olivier Simonin, Pascal Fede In this work we characterize the particle temperature distribution of inertial particles interacting with a turbulent non-isothermal flow. In the general frame of the mesoscopic Eulerian approach developed by Fevrier et al. [\emph{J. Fluid Mech.}, {533}, 1-46] for the particle velocity distribution, we show that the instantaneous particle temperature can be partitioned in two different contributions. The first contribution is a continuous temperature field shared by all the particles and taking into account two-point correlations. The second is a random spatially uncorrelated contribution, characterized in terms of Eulerian fields of particle moments. This conclusion is pointed out through statistical one-point and two-point correlation analysis. Statistics are measured from numerical simulations of particles suspended into a homogenous, isotropic, stationary non- isothermal turbulence where discrete particle paths are computed by Lagrangian tracking. The goal of this work is to improve the comprehension of mechanisms of heat transfer and transport for the development of unsteady Eulerian modelling approaches for reactive two-phase flows. The local instantaneous Eulerian equations for the mesoscopic temperature and the random uncorrelated heat flux are derived. We also point out that temperature distribution is related to the both dynamical and thermal particle response times. [Preview Abstract] |
Tuesday, November 24, 2009 9:18AM - 9:31AM |
MK.00007: Particle motion in a turbulent serpentine channel Xin Huang, Paul Durbin Particle motion in serpentine passage was studied using direct numerical simulation coupled with Lagrangian particle tracking. In a straight, turbulent channel, eddies are responsible for particle deposition in the near-wall region. In a serpentine channel, particle inertia may be the dominant cause of high concentration near the outer bend in the curved section. However, turbulent convection is still important. This depends on the relative magnitude of particle Stokes number and turbulent time-scale. Particles with small Stokes number form a plume that leaves the inner bend and high concentration layers near both walls in the straight section before entering the bend. The high concentration layers remain thin, reminiscent of plane channel flow. Significant deposition of heavier particles in the straight section is only found on the side extended from the outer bend. There are two plumes at the entrance of bend because of the larger particle inertial and thicker layer of high concentration. Particle deposition in the curved section is also affected by particle-wall collision and simulation results of particulate impact and erosion will be presented. [Preview Abstract] |
Tuesday, November 24, 2009 9:31AM - 9:44AM |
MK.00008: Incipient motion of spherical particles induced by a vortex ring disturbance Maria-Laura Beninati, Michael McErlean, Michael Krane, Arnold Fontaine Experiments to characterize the ability of a vortical disturbance to induce incipent motion of a stationary particle resting on a horizontal planar surface are described. The ultimate goal of this study is to assess the role of turbulent boundary layer coherent structures in particle suspension. In this study, a vortex ring plays the role of a model flow disturbance because its compact, three-dimensional structure and speed are easily controlled and characterized. The vortex rings are generated by injecting a slug of fluid at a specified height above the ground plane. The vortex ring and its motion are described in terms of the convection speed, size, and circulation, using a combination of high-speed video and DPIV. The flow disturbance at the wall is characterized using wall pressure measurements during the passage of the vortex ring. These measurements are used to determine the relationship between the measures of the vortex ring disturbance and the resulting pressure fluctuation at the wall. Finally the ability of a vortex ring of known strength and convection path to induce motion to a single particle placed on the ground plane is assessed using high-speed video. [Preview Abstract] |
Tuesday, November 24, 2009 9:44AM - 9:57AM |
MK.00009: Optical measurements of jet gas and bed particle velocity distributions in a 2D bubbling fluidized bed Alexander Mychkovsky, Steven Ceccio A laser Doppler velocimetry (LDV) measurement technique has been developed to obtain spatially and temporally resolved measurements of jet gas and bed particle velocities in a 2D bubbling fluidized bed. The LDV system was configured to eliminate spurious optical intensity fluctuations, which can contaminate velocity measurements in optically dense flows. The jet gas was seeded with ice crystals, which were formed by rapidly condensing and freezing the moisture in the jet air just prior to injection. LDV bursts from the bed particles and gas tracer ice crystals were simultaneously recorded to obtain the particulate and gas phase velocities at a given location within the jet plume in a non-intrusive manner. [Preview Abstract] |
Tuesday, November 24, 2009 9:57AM - 10:10AM |
MK.00010: Particle Capture by a Conducting Cylinder in an Electrostatic Field using a Discrete Element Method Guanqing Liu, Shuiqing Li, Jeffrey Marshall Particle capture by a conducting cylinder is studied with a discrete element method (DEM) developed for particle transport with electrostatic effects. A charged cylinder is placed in a uniform electric field. Uncharged particles are advected toward the cylinder by air flow. Electric field generation by the cylinder is resolved by a boundary element method (BEM), which accounts for effect of polarized particles on the cylinder induced surface charge. Conventional BEM exhibits errors when near-surface particles are smaller than BEM panels. An algorithm using approximate particle images and local panel subdivision is introduced to improve computational accuracy. Particle-particle electrostatic interaction is accelerated using a fast multipole expansion method. The simulation shows that particles captured by the cylinder form straight chains oriented nearly perpendicular to the cylinder surface. Varying the cylinder voltage with fixed uniform electric field strength leads to different particle deposition characteristics. Particles deposit on only one side of the cylinder at low voltages, but at higher voltages particles deposit all over the cylinder. Predicted particle capture efficiency compares well with experimental data. [Preview Abstract] |
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