Settling dynamics of Kolmogorov scale sediment particles in homogeneous isotropic turbulence

Settling dynamics of slightly heavier-than-fluid particles in turbulence is of critical importance for suspended sediment transport. Of particular interest is the mean particle settling velocity in turbulence which can be influenced by fast tracking, vortex trapping, and loitering mechanisms. A point-particle model based on the complete Maxey-Riley equation is used to investigate settling dynamics of particles in vortical flows. First, particles settling in a stationary Taylor-Green vortex is investigated by varying the vortex strength relative to the particle settling speed in quiescent flow. For medium vortex strength, the settling speeds are observed to decrease due to loitering and vortex trapping effects. Fast tracking dominates and increases the settling speed for higher vortex strengths. This behavior is further investigated in a two-way coupled, forced, homogeneous isotropic turbulence by varying the turbulence intensity relative to the settling speed in quiescent flow for multiple Stokes numbers, in order to characterize the settling dynamics of Kolmogorov-scale particles. Mechanisms that influence the settling dynamics for a range of turbulence intensity and particle Stokes numbers are identified.