Behavior of settling particles in homogeneous shear turbulence

In this study, particle-laden shear turbulence is investigated by performing direct numerical simulation under a point-particle approximation for spherical heavy particles with a diameter smaller than the Kolmogorov length scale of the flow. The ranges of the Stokes number and gravity factor considered in our study are St=0.1,0.5,1,5, and 10 and W(=vt/vη)=0,10,20,30, and 40, respectively, where vt and vη are the terminal velocity and the Kolmogorov velocity scale, respectively. The behavior of settling particles is investigated by introducing a two-dimensional distribution function to quantify the anisotropic clustering. A principal component analysis of the two-dimensional distribution evidently indicates that the preferential orientation of clustering at different scales is identified well. Small-scale clustering displays a multifractal nature with an explicit angular distribution.