Large Eddy Simulation and Second-Moment Closure Model of Particle Fluctuating Motion in Two-Phase Turbulent Shear Flows

Turbulence statistics of non-settling discrete solid particles suspended in homogeneous turbulent gas shear flows generated by means of large eddy simulation (LES) are investigated for two different mean shear rates (S = 25 and 50 /s) and three different particle diameters (d = 30, 45 and 60 μm). Concurrently, a second-moment closure model of the particle fluctuating motion, based on separate transport equations for the particle kinetic stresses and the fluid-particle velocity correlations, is described and the corresponding predictions are compared with the simulation results. Large eddy simulation and closure model predictions show that the most noticeable effect of inertia is to increase the degree of anisotropy of the particle fluctuating motion with respect to the fluid one. As a matter of fact, the transverse particle turbulent velocity components are directly controlled by the dragging by the fluid turbulence and decrease with increasing particle relaxation time compared to the fluid turbulence integral time scale. In contrast, the streamwise component increases, due to the influence of both the fluid and particle mean velocity gradients, and eventually exceeds the corresponding gas turbulent component.