Settling and clustering of particles of moderate mass density in turbulence

TL;DR

This numerical study investigates how small inertial particles with moderate density differences behave in turbulence, focusing on their settling, clustering, and velocity statistics under varying gravity and mass ratios.

Contribution

It explores the combined effects of fluid-to-particle mass ratio and gravity on particle dynamics, revealing non-monotonic behaviors and clustering trends not previously detailed.

Findings

Velocity skewness and kurtosis vary non-monotonically with parameters.

Clustering increases with gravitational acceleration.

Settling velocity shows anomalous behavior compared to free-fall Stokes velocity.

Abstract

We present a numerical study of settling and clustering of small inertial particles in homogeneous and isotropic turbulence. Particles are denser than the fluid, but not in the limit of being much heavier than the displaced fluid. At fixed Reynolds and Stokes numbers we vary the fluid-to-particle mass ratio and the gravitational acceleration. The effect of varying one or the other is similar but not quite the same. We report non-monotonic behavior of the particles' velocity skewness and kurtosis with the second parameter, and an associated anomalous behavior of the settling velocity when compared to the free-fall Stokes velocity, including loitering cases. Clustering increases for increasing gravitational acceleration, and for decreasing fluid-to-particle mass ratio.