The Scallop Theorem and Swimming at the Mesoscale

TL;DR

This paper demonstrates that at the mesoscale, asymmetric self-propelling objects can bypass the scallop theorem by exploiting fluid inertia differences, enabling propulsion despite reciprocal deformation.

Contribution

It introduces a novel mechanism where fluid inertia and asymmetry enable self-propulsion, challenging the classical scallop theorem at the mesoscale.

Findings

Asymmetric dumbbell propels despite reciprocal motion.

Fluid inertia can be separated from swimmer inertia at mesoscale.

Asymmetry in coasting times creates non-reciprocal flow fields.

Abstract

By synergistically combining modeling, simulation and experiments, we show that there exists a regime of self-propulsion in which the inertia in the fluid dynamics can be separated from that of the swimmer. This is demonstrated by the motion of an asymmetric dumbbell that, despite deforming in a reciprocal fashion, self-propagates in a fluid due to a non-reciprocal Stokesian flow field. The latter arises from the difference in the coasting times of the two constitutive beads. This asymmetry acts as a second degree of freedom, recovering the scallop theorem at the mesoscopic scale.