Numerical simulations of the two-dimensional backward facing step gas-particle turbulent flow are reported. Both the evolution of large eddy coherent structures in spatially and temporally and the vortex-particle interactions are researched. Effects of the particle Stokes number and the initial two-phase velocity slip on the instantaneous concentration distribution of the particles with and without the influence of gravity are discussed. Continuous phase simulation is performed by the method of large eddy simulation (LES) while the particle phase is solved by a Lagrangian method. Simulations of the gas phase reproduce the character of the separation and reattachment flow and the essential features of the coherent structures. It is shown that the vortex structures become extraordinary abundant and complex under the high Reynolds number. Further more, the simulation shows the initial two-phase velocity slip plays an important role in enforcing particle dispersion and sharply changes the instantaneous particle distribution under the different particle Stokes numbers. Even more, results demonstrate the influence of gravity on particle dispersion and sedimentation. Such pronounces effect of gravity on instantaneous concentration of particles with increased Stokes number and initial slip coefficients emphasize the need for the consideration of gravity for horizontal particle-laden flow. Either the continuous phase results or particle phase results obtained from LES agree well with the experiment data both in quantitative and qualitative.

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