Sedimenting Elastic Filaments in Turbulent Flows

TL;DR

This study examines how elastic filaments settle in turbulent flows, revealing that turbulence increases average settling speed, elasticity affects tumbling behavior, and fluctuations follow a power-law dependence on filament weight.

Contribution

It provides new insights into the interplay between elasticity, turbulence, and sedimentation dynamics of filaments, highlighting the role of flow-induced tumbling and stretching.

Findings

Mean settling velocity is moderately increased by turbulence.

Tumbling frequency is linked to filament elasticity and follows a Poisson process.

Velocity fluctuations depend on filament weight, not elasticity.

Abstract

We investigate the gravitational settling of a long, model elastic filament in homogeneous isotropic turbulence. We show that the flow produces a strongly fluctuating settling velocity, whose mean is moderately enhanced over the still-fluid terminal velocity, and whose variance has a power-law dependence on the filament's weight but is surprisingly unaffected by its elasticity. In contrast, the tumbling of the filament is shown to be closely coupled to its stretching, and manifests as a Poisson process with a tumbling time that increases with the elastic relaxation time of the filament.