MOTIONS OF SMALL PARTICLES IN A TURBULENT SIMPLE SHEAR-FLOW FIELD UNDER MICROGRAVITY CONDITION

Motions of small rigid spheres in a turbulent flow field in the presence of a uniform mean shear and in the absence of gravitational effect are studied. The particle equation of motion, which includes the Stokes drag and the Saffman lift force effects, is treated as a stochastic differential equation. The spectral method is used and analytical expressions relating the components of particle response statistics to that of the flow field are developed. The particle spectral intensities, autocorrelation functions, and mean-square velocities, as well as particle diffusivities for different particle relaxation times and mean shear rates are evaluated. It is shown that the presence of a mean shear field enhances the particle diffusivity in the transverse direction. Experimental observations of particle mass diffusivity greater than that of the fluid particle may then be explained by this shear-induced enhancement.