Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session G8: Particle-Laden Flows IV: General Topics |
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Chair: Dimitrios V. Papavassiliou, University of Oklahoma Room: 330 |
Monday, November 25, 2013 8:00AM - 8:13AM |
G8.00001: Effects of near-wall turbulence structure on particles of different Schmidt number Quoc Nguyen, Chiranth Srinivasan, Dimitrios Papavassiliou The simulation of the trajectories of scalar particles with different Schmidt numbers, Sc, in turbulent channel flow shows that the effects of near-wall turbulence can lead to significantly different transport behavior for different Sc particles. The reason is that different parts and different scales of the coherent near-wall structures contribute to the transport of particles of different Sc. When particles enter the flow field from a common location at the channel wall, these interactions lead to the observation of different concentrations of particles downstream from the source, depending on their Sc and on time. While this is expected based on intuition, it is a rather interesting finding because it opens the possibility to separate particle dispersions according to their Sc using turbulence. A minimum difference in Sc is required, so that distinct transport mechanisms contribute to the transfer of each type of particle. Results from direct numerical simulation at friction Reynolds number of 300 and 600 will be discussed and for Sc that covers five orders of magnitude. [Preview Abstract] |
Monday, November 25, 2013 8:13AM - 8:26AM |
G8.00002: Hydrodynamic forces between colliding spheres during mechanical contact Julian Simeonov The time-dependent Stokes equations are solved in the gap of O(1 mm) colliding spheres to determine the rate of change of the lubrication forces after the onset of mechanical contact and large deceleration. Mechanical contact is assumed to begin when the gap clearance becomes equal to the size of the O(0.1 micron) micro-asperities present on the surface of real particles. Fourier expansion is used to solve the initial value problem. Assuming small gap clearances, the leading order asymptotic solution is obtained using singular perturbation expansion methods to match the viscous gap solution and the outer inviscid solution. The asymptotic solution provides the dependence of the resistance, added mass and history forces on the sphere velocity, sphere acceleration, the micro-asperity size and the ratio of the sphere diameters. The analytical results can be used to improve the modeling of hydrodynamic forces during mechanical contact in simulations of particle-laden flow or acoustic propagation in fully saturated sediments. [Preview Abstract] |
Monday, November 25, 2013 8:26AM - 8:39AM |
G8.00003: Eulerian-Lagrangian large eddy simulations of dense liquid-solid slurry flow through a horizontal pipe Sunil Arolla, Jesse Capecelatro, Olivier Desjardins A high-fidelity large eddy simulation based Eulerian-Lagrangian methodology is used to investigate the detailed dynamics of liquid-solid slurries in a horizontal pipe. A dynamic Smagorinsky model based on Lagrangian averaging is employed to account for the sub-grid scale effects in the liquid phase. A fully conservative immersed boundary method is used to account for the pipe geometry on a uniform cartesian grid. The liquid and solid phases are coupled through volume fraction and the momentum exchange terms. Particle-particle and particle-wall collisions are modeled using a soft-sphere approach. Mean particle concentration and velocity profiles are computed, showing excellent agreement with experimental data. Covariance statistics are extracted and compared against multiphase turbulence models in the literature. When the bulk liquid velocity is below the critical deposition velocity, particles form a static bed at the bottom that exhibits strong size segregation. Based on our numerical simulations, a critical value for the Froude number is proposed below which the solid particles starts depositing. [Preview Abstract] |
Monday, November 25, 2013 8:39AM - 8:52AM |
G8.00004: Decoupling the effects of the streamline curvature and the vorticity on the hydrodynamic forces acting on a spherical particle in rotating flows Toshiaki Fukada, Shintaro Takeuchi, Takeo Kajishima Understanding fluid-particle interactions in vortical flows is important for predicting and controlling particle-laden flows. In the present study, the angular velocity and the lift force on the particle in a free vortex (irrotational flow) and a forced vortex (rigidly-rotating flow) are studied by numerical simulation to see the effects of the streamline curvature and the vorticity of the background flows. Based on the non-inertial frame of reference fixed at the particle center, the streamline curvature and particle Reynolds number of the background flows are varied. An original convective boundary condition is proposed for the curved background flows. For both free and forced vortices, the angular velocity of the particle shows self-similar profile with respect to the streamline curvature of the background flow, and the angular velocity is decomposed into two independent contributions of the streamline curvature and the vorticity. As for the lift coefficient, which also exhibits self-similarity with respect to the streamline curvature, the contributions of the streamline curvature, the vorticity and the angular velocity of the particle are decoupled, and a unified correlation equation for both vortices is proposed. [Preview Abstract] |
Monday, November 25, 2013 8:52AM - 9:05AM |
G8.00005: Particle interaction in oscillatory Couette and Poiseuille flows Nima Fathi, Marc Ingber, Peter Vorobieff In oscillating Poiseuille flows of relatively dense suspensions, the direction of particle migration changes with the amplitude of oscillation. High amplitudes produce migration toward low shear rate regions of the flow, and vice versa, low oscillation amplitude results in particle migration toward the high shear rate region. We demonstrate that a similar behavior can be observed in a two-particle system, where it can be physically interpreted more easily, and discuss numerical modeling and experimental studies of oscillatory Poiseuille and Couette flows. [Preview Abstract] |
Monday, November 25, 2013 9:05AM - 9:18AM |
G8.00006: On the simulation of turbulent particle-laden flow subject to radiation: Comparison between Eulerian and Lagrangian approaches Aymeric Vie, Hadi Pouransari, Remi Zamansky, Ali Mani The objective of this work is to assess the range of applicability of Eulerian particle transport solvers for radiatively driven particle-laden flows with applications in particle solar receivers and cloud dynamics. In particular we consider a triply periodic flow laden with particles subject to homogeneous radiation [studied by Zamansky et. al. 2013]. Heat transfer from particle clusters to the carrier gas generates buoyancy effects, which leads to vorticity generation in the carrier phase. The vortical structures induce preferential concentration and cluster modification. This feedback dynamics leads to a self-sustained state of turbulence. We present numerical investigation of this configuration using both Lagrangian particle models and Eulerian moment methods (EMM). For the Eulerian moment method, the particle density and momentum are solved using different numerical schemes under the monokinetic assumption. We compare the results obtained by both approaches varying the Stokes number, the particle loading as well as the mesh refinement. [Preview Abstract] |
Monday, November 25, 2013 9:18AM - 9:31AM |
G8.00007: Radiative heating of a turbulent particle-laden flow: Effects of radiation regimes on turbulence dynamics Ari Frankel, Hadi Pouransari, Gianluca Iaccarino, Ali Mani Radiation transport modeling has become increasingly important in the design and analysis of advanced thermal-fluid systems such as particle solar receivers. However, the mechanism for the two-way coupling of radiation transport with turbulence and particle dynamics has not been explored. In this work we employed algebraic and differential radiation models in direct numerical simulations of turbulence particle-lade flows subject to external radiative sources. It is shown that different radiation regimes, from optically thin to opaque, lead to significantly different turbulence structures and particle aggregation. [Preview Abstract] |
Monday, November 25, 2013 9:31AM - 9:44AM |
G8.00008: Characterization of the temporal evolution of the particle clustering in radiation-induced turbulence R\'emi Zamansky, Ali Mani In the context of particles laden flow, we explore a regime in which turbulence is sustained solely by the radiative energy absorbed by the dispersed phase. Under such conditions, the non-uniformities in particle distribution produce local temperature fluctuations. In response, the resulting buoyancy induced vortical fluid motions alter the particles concentration. From numerical simulations it has been shown that the feedback loop between the local particle concentration, the temperature fluctuations and the convective motion can create and sustain turbulence in a wide range of parameters, whose key parameter is the particle response time. In particular the temperature variance as well as the turbulent kinetic energy present a sharp peak for maximum particle clustering. The time scales of the temperature and momentum forcing are therefore highly influenced by the ``clusters life time.'' We employed a method that enables to track the temporal evolution of clusters and detect the clusters merging and splitting. This approach uses the Voronoi tessellation of the particle positions (and the connectivity of its cells) to detect the clusters. By introducing a cluster-cluster correlation we construct a random graph representative of the cluster temporal evolution. [Preview Abstract] |
Monday, November 25, 2013 9:44AM - 9:57AM |
G8.00009: A low-Mach approximation computational framework for particle-laden flows subject to radiation Hadi Pouransari, Remi Zamansky, Ali Mani The three-way coupled physics of radiation, fluid flow, and particle transport forms the dynamical ingredients in various technological and natural systems, such as particle-based solar-thermal systems, clouds, soothing flames, and atmospheric aerosols. Depending on radiation intensity, the density fluctuations in such systems can be up to order of the mean density itself. We present a parameterization of this problem using a simple model considering flow laden with particles with finite momentum relaxation time. We further present a coupled computational algorithm for simulation of flow, particle transport, and heat transfer using low-Mach approximation. Variety of statistics for gas and dispersed phases are investigated to depict the effect of radiation on particle-laden turbulence at different scenarios. The range of applicability of Boussinesq approximation for modeling buoyancy effects will be discussed. [Preview Abstract] |
Monday, November 25, 2013 9:57AM - 10:10AM |
G8.00010: Large-Eddy Simulation of Particle Dispersion Inside and Above Plant Canopies Ying Pan, Marcelo Chamecki, Scott Isard Modeling the dispersion of small particles such as pathogenic spores, pollens, and small seeds inside and above plant canopies is important in many applications. Transport of these particles is driven by strongly inhomogeneous, coherent, and non-Gaussian turbulent flows inside the canopy roughness sublayer (the regions extending from ground to about three canopy heights). We develop an LES approach that includes parameterization of plant reconfiguration through a velocity-dependent drag coefficient and yield predictions of turbulence statistics and coherent structures in good agreement with experimental data. Particle dispersion is also validated against experimental data of spore dispersal inside and above a maize field. LES results are used in the development of a simple framework for modeling the particle plume. Characteristics of the particle plume in the near and far fields are studied. Results suggest that the far field plume can be approximated by a simple analytical solution if the fraction of spores that escape the canopy region is known. [Preview Abstract] |
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