A new form of mixing in turbulent sedimentation

TL;DR

This paper introduces a novel convective mixing regime in sedimentation of inertial particles, characterized by an accelerating mixing layer and a new modeling approach, revealed through advanced numerical simulations.

Contribution

It uncovers a new sedimentation regime with an anomalous mixing layer growth and develops a 1D model based on hindered settling law to describe it.

Findings

Mixing layer accelerates with a non-integer exponent.

Bulk region moves at a constant velocity.

Model accurately predicts the dynamics based on density ratio.

Abstract

We study the sedimentation of finite-size inertial particles in a Rayleigh-Taylor-like setup using state-of-the-art direct numerical simulations. The falling particles are observed to produce two distinct regions: a leading mixing layer with a linear concentration profile followed by a bulk region of uniform density. Unlike classical RT turbulence, the mixing layer extension accelerates with an anomalous, non-integer exponent, while the bulk region moves at a constant velocity. A one-dimensional model based on a local hindered settling law accurately captures the observed dynamics and its dependence on the particle-to-fluid density ratio. The present work identifies a new regime of convective mixing which develops at the front of particle suspensions in sedimentation processes.