Behavior of heavy particles in shear turbulence under gravity

This study is aimed at investigation of particle-laden shear turbulence under gravity using direct numerical simulation. The Navier-Stokes equation was numerically solved on 128³ grids using a pseudo-spectral scheme on shear-periodic cubic domain to describe homogeneous shear turbulence at Re_λ=67 and the shear parameter S^* ~ 7. The equation of particle motion was solved by taking into account the linear Stokes drag and gravity together. The twenty-five cases were simulated for the Stokes number, St = 0.1, 0.5, 1, 5, 10 and the gravity factor, W= 0, 10, 20, 30, 40. Clustering of particles occurs when Stokes number is around 1 without gravity by shearing motion. We found, however, as gravity is applied to particles of St =1, the clustering effect seems to weaken slightly, and the particles tend to align with shear direction. When Stokes number is higher than 1 without gravity, the particles are almost randomly distributed. However, when heavy particles with St=5 settle under strong gravity (W=40), a string pattern of particle clustering is clearly observed. A different pattern of clustering due to gravity is clearly discernible from the cases without gravity. Detailed statistics of particles motion and a plausible physical mechanism will be discussed in the presentation.