Passive swimming in low Reynolds number flows

TL;DR

This paper explores how microscopic swimmers can extract energy from external flows to move across low Reynolds number environments, revealing a new mechanism that bypasses the scallop theorem.

Contribution

It introduces a novel swimming mechanism based on energy extraction from external flows, extending the understanding of low Reynolds number locomotion.

Findings

Migration velocity scales linearly with stroke amplitude

Energy extraction mechanism generalizes vesicle tank-treading

Scallop theorem does not apply in external flow fields

Abstract

The possibility of microscopic swimming by extraction of energy from an external flow is discussed, focusing on the migration of a simple trimer across a linear shear flow. The geometric properties of swimming, together with the possible generalization to the case of a vesicle, are analyzed.The mechanism of energy extraction from the flow appears to be the generalization to a discrete swimmer of the tank-treading regime of a vesicle. The swimmer takes advantage of the external flow by both extracting energy for swimming and "sailing" through it. The migration velocity is found to scale linearly in the stroke amplitude, and not quadratically as in a quiescent fluid. This effect turns out to be connected with the non-applicability of the scallop theorem in the presence of external flow fields.