Clustering and relative velocities of heavy particles under gravitational settling in isotropic turbulent flows
arXiv:1507.07278
Abstract
Spatial clustering and intermittency in the relative velocity of heavy particles of the same size settling in turbulent flows can be strongly affected by gravity. We present a model for the timescale of the fluid velocity gradient seen by particle pairs and propose an effective Kubo number based on this timescale to explain the mechanism of gravity-enhanced clustering. We explore the mechanisms of the gravity-induced reduction or enhancement of the intermittency in the particle radial relative velocity (RRV) at different Stokes numbers based on backward-in-time relative dispersion and preferential sampling of the fluid field. These effects of gravity on clustering and the RRV must be parameterized in the geometric collision kernel.
10 pages, 5 figures