Extensibility enables locomotion under isotropic drag

TL;DR

This paper demonstrates that extensible slender bodies can achieve locomotion under isotropic viscous drag, challenging the common belief that anisotropic drag is necessary for low Reynolds number swimming.

Contribution

It introduces the concept that extensibility can enable propulsion without drag anisotropy, supported by analytical models of a two-ring swimmer and a dinoflagellate flagellum.

Findings

Locomotion under isotropic drag is possible with extensible bodies.

Extensibility provides a new mechanism for self-propulsion.

Potential applications in complex fluid environments with weak drag anisotropy.

Abstract

Anisotropic viscous drag is usually believed to be a requirement for the low Reynolds number locomotion of slender bodies such as flagella and cilia. Here we show that locomotion under isotropic drag is possible for extensible slender bodies. After general considerations, a two-ring swimmer and a model dinoflagellate flagellum are studied analytically to illustrate how extensibility can be exploited for self-propulsion without drag anisotropy. This new degree of freedom could be useful for some complex swimmer geometries and locomotion in complex fluid environments where drag anisotropy is weak or even absent.