The transient swimming of a waving sheet

TL;DR

This paper derives the transient swimming speed and fluid flow around a waving sheet at low Reynolds numbers, extending classic steady-state models to include initial startup dynamics.

Contribution

It introduces the first analysis of transient effects in the low-Reynolds number swimming of a waving sheet, including startup from rest.

Findings

Transient swimming speed is characterized for the first time.

Time scales for transient effects are derived using physical arguments.

Results extend steady-state models to include initial startup dynamics.

Abstract

Small-scale locomotion plays an important role in biology. Different modelling approaches have been proposed in the past. The simplest model is an infinite inextensible two-dimensional waving sheet, {originally introduced by Taylor}, which serves as an idealized geometrical model for both spermatozoa locomotion and ciliary transport in Stokes flow. Here we complement classic steady-state calculations by deriving the transient low-Reynolds number swimming speed of such a waving sheet when starting from rest (small-amplitude initial-value problem). We also determine the transient fluid flow in the `pumping' setup where the sheet is not free to move but instead generates a net fluid flow around it. The time scales for these two problems, which in general govern transient effects in transport and locomotion at low Reynolds numbers, are also derived using physical arguments.