Soft swimming: Exploiting deformable interfaces for low-Reynolds number locomotion

TL;DR

This paper demonstrates that reciprocal swimming motions can induce locomotion near deformable interfaces at low Reynolds numbers, leveraging interface deformation to overcome the constraints of reciprocal movement.

Contribution

It introduces a novel mechanism where nonlinear interfacial deformation rectifies reciprocal flows, enabling locomotion near deformable interfaces, supported by theoretical analysis and macro-scale experiments.

Findings

Reciprocal motion can cause movement near deformable interfaces.

Interface deformation breaks the symmetry of reciprocal flows.

Experimental validation with macro-scale flapping motion.

Abstract

Reciprocal movement cannot be used for locomotion at low-Reynolds number in an infinite fluid or near a rigid surface. Here we show that this limitation is relaxed for a body performing reciprocal motions near a deformable interface. Using physical arguments and scaling relationships, we show that the nonlinearities arising from reciprocal flow-induced interfacial deformation rectify the periodic motion of the swimmer, leading to locomotion. Such a strategy can be used to move toward, away from, and parallel to any deformable interface as long as the length scales involved are smaller than intrinsic scales, which we identify. A macro-scale experiment of flapping motion near a free surface illustrates this new result.