Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session HE: Multiphase Flows: General I |
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Room: Hilton Chicago Continental B |
Monday, November 21, 2005 1:20PM - 1:33PM |
HE.00001: Point-Force Energy Coupling Tristan Burton, Kyle Squires Fully resolved simulations of particle-laden turbulent flows are computationally expensive even with a single particle. Therefore, simulations of flows with realistic numbers of particles typically treat the disperse phase as point-particles and models are used to account for the interaction between the phases. The particle trajectories are determined using a Lagrangian particle equation of motion that accounts for the fluid forces. The effect of the particulate phase on the fluid is included using point-force momentum coupling, where the opposite of the force applied to each particle by the fluid is distributed back to fluid grid points in a local region. In this work, we perform direct numerical simulation (DNS) of a particle moving at a prescribed constant or time-dependent velocity through a stationary fluid, and use the resulting force history in a corresponding point-force simulation to study point-force energy coupling. The energy input from the moving particle and the fluid dissipation in the DNS are compared to corresponding quantities in the unresolved calculation. A range of particle Reynolds numbers and ratios of the particle diameter to the unresolved grid spacing are considered to determine the conditions under which point-force momentum coupling provides accurate energy coupling. [Preview Abstract] |
Monday, November 21, 2005 1:33PM - 1:46PM |
HE.00002: Direct Numerical Simulation of Multiphase Isotropic Turbulence with O(100) Embedded Spheres Lin Zhang, S. Balachandar, Paul Fischer The problem of particle turbulence interaction is of fundamental importance. However its theoretical and computational studies have been generally limited to dilute dispersion of very small particles. Our understanding of this problem in the regime where the particles are of {\em{finite-size}}, of the order of Taylor microscale, has been quite limited. In particular, effect of turbulence on the lift and drag forces on the particles, back effect of particles on carrier phase turbulence, and the inter particle effect within a distribution, are all open questions in the context of finite-sized particles. A novel technique is used to generate high quality body-fitted hexahedral mesh around a distribution of O(100) spheres in an automated way. This mesh along with a higher-order accurate Spectral-Element-Methodology (SEM) is used in the {\em{fully resolved}} simulations of forced isotropic turbulence with the distribution of embedded spheres. We employ a very fine discretization and the quality of results parallel those of fully spectral simulations of single phase isotropic turbulence. We perform simulations with and without the distribution of embedded spheres and employ the same random forcing in both. By comparing results the modification of the turbulence field due to the spheres, forces on the particles, and vortex structures around particles will be addressed. [Preview Abstract] |
Monday, November 21, 2005 1:46PM - 1:59PM |
HE.00003: Numerical investigation of meso-scale structures using a two fluid model with non-Newtonian closure Jos\'{e} Miguel Perez, Alfredo Pinelli The idea is based on identifying the physical roles of the solid and fluid stress tensors in the solid phase momentum equation. The tensors are reformulated as a sum of different terms. A comparison with the closure proposed by Marchioro et al. (Int. J. Multiphase flow. 27: 237-276, 2001), leads to a new non-Newtonian closure. The complete model has been tested with two different scenarios. First, we used an initial Taylor-Green base flow for the fluid phase with a highly diluted regime with mass fraction of order one. This case allows for a critical evaluation of the present formulation vs Saffman's 1962. We also considered a base channel flow with solid particles. Different regimes (solid fractions) have been considered. The results are compared vs Agrawal et al. (J. Fluid Mech. 445: 151-185, 2001) in terms of of meso-scale solid structures behaviours. The numerical discretization for both phases is based on a finite volume formulation using a Rusanov scheme for the hyperbolic part of the equations that preserves the positivity of the void fraction. [Preview Abstract] |
Monday, November 21, 2005 1:59PM - 2:12PM |
HE.00004: A nonlinear Riemann solver for non-conservative two-phase flow models Vincent Deledicque, Miltiadis Papalexandris Hydrodynamic models for two-phase flows of gas -- solid particle mixtures typically consist of the mass, momentum, and energy balance equations for each phase, supplemented by an evolution equation for the solid volume fraction. Such models are non- conservative due to the so-called nozzling terms that appear in the expressions for the interactions between the two phases. In this talk we present a non-linear (exact) Riemann solver for such flow models. In general, the solution of this Riemann problem consists of 6 distinct nonlinear waves (the solid phase velocity is a double eigenvalue): shocks, rarefactions and contact discontinuities. Therefore, for given end-states there exists a large number of possible wave configurations. Our numerical method is based on a suitable grouping of them into 4 principal families of configurations. Numerical solutions are obtained via an iterative procedure in which these families are examined sequentially. Comparisons between numerical and exact solutions are presented to demonstrate the efficacy of the proposed method. Finally, the issue of the non-uniqueness of solution to the Riemann problem is briefly discussed. [Preview Abstract] |
Monday, November 21, 2005 2:12PM - 2:25PM |
HE.00005: Boundary layers in dilute particle suspensions M.R. Foster, P.W. Duck, R.E. Hewitt Boundary layers in dilute particle suspensions have been found to have a number of interesting features. The development of a singularity at the wall has recently been found to be common to many of these flows, \footnote{See Foster, Duck \& Hewitt, {\it J. Fluid Mech.} {\bf 474} (2003) and Duck, Hewitt \& Foster, {\it J. Fluid Mech.} {\bf 514}, (2004)} and we note here that Falkner-Skan-type boundary layers (layers with `edge' velocity proportional to $x^m$) and the boundary layer under a linearly decelerating flow \footnote{Howarth (1934)} also break down at the wall in the absence of gravity, but can be singularity-free for heavy particles. In addition, we find that matching of the Falkner-Skan profile to an outer flow is problematic for some values of $m$, though the case most studied heretofore---the Blasius case (for $m=0$)---does not feature this difficulty. Finally, a boundary layer that does not develop a singularity takes on a the typical Falkner-Skan self-similarity far downstream, in the absence of gravity. For heavy particles, however, gravity causes a constant drift of particles toward the wall, and a constant-thickness far-downstream layer. The far-downstream behavior in a light-particle suspension is different, with a particle-free zone between the wall and a particle `shock' that grows like $x^{(1-m)}$. [Preview Abstract] |
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