Large-scale confinement and small-scale clustering of floating particles in stratified turbulence

TL;DR

This study models and simulates the behavior of small inertial particles in stratified turbulence, revealing how stratification influences vertical confinement while particle relaxation time affects small-scale clustering, with implications for phytoplankton layer formation.

Contribution

The paper introduces a simplified model for inertial particle dynamics in stratified turbulence and provides extensive numerical analysis of particle distribution and clustering behaviors.

Findings

Vertical confinement is mainly controlled by stratification strength.

Small-scale clustering depends on particle relaxation time.

Clustering is nearly independent of flow stratification.

Abstract

We study the motion of small inertial particles in stratified turbulence. We derive a simplified model, valid within the Boussinesq approximation, for the dynamics of small particles in presence of a mean linear density profile. By means of extensive direct numerical simulations, we investigate the statistical distribution of particles as a function of the two dimensionless parameters of the problem. We find that vertical confinement of particles is mainly ruled by the degree of stratification, with a weak dependency on the particle properties. Conversely, small scale fractal clustering, typical of inertial particles in turbulence, depends on the particle relaxation time and is almost independent on the flow stratification. The implications of our findings for the formation of thin phytoplankton layers are discussed.