The waltz of tiny droplets and the flow they live in

TL;DR

This paper investigates the behavior of tiny inertial particles in vortex flows, highlighting caustic formation's role in particle collisions, cloud rain initiation, and turbulence dynamics, with implications for understanding droplet growth.

Contribution

It introduces new insights into caustic formation effects in vortex flows and estimates their significance in turbulence and cloud processes, including rain formation.

Findings

Caustics significantly influence particle collisions.

Estimates of caustics' role in high Reynolds turbulence.

Potential impact of phase change on cloud turbulence.

Abstract

This article describes the dynamics of small inertial particles centrifuging out of a single vortex. It shows the importance of caustics formation in the vicinity of a single vortex: both for particle collisions and void formation. From these single-vortex studies we provide estimates of the role of caustics in high Reynolds number turbulence, and in the case of clouds, estimate how they may help in rain initiation by bridging the droplet-growth bottleneck. We briefly describe how the Basset- Boussinesq history force may be calculated by a method which does not involve huge memory costs, and provide arguments for its possible importance for droplets in turbulence. We discuss how phase change could render cloud turbulence fundamentally different from turbulence in other situations.