Transition in swimming direction in a model self-propelled inertial swimmer

TL;DR

This paper models a self-propelled swimmer at intermediate Reynolds numbers, demonstrating how steady streaming flows enable propulsion and directional reversal as Re increases, highlighting SS as a key motility mechanism.

Contribution

It introduces a reciprocal swimmer model with oscillating spheres that shows flow-driven propulsion and direction switching at intermediate Re, emphasizing steady streaming flows' role.

Findings

Swimmer propels via nonlinear steady streaming flows.

Swimming direction reverses at a critical Reynolds number.

Steady streaming flows are crucial for motility at intermediate Re.

Abstract

We propose a reciprocal, self-propelled model swimmer at intermediate Reynolds numbers ($Re$). Our swimmer consists of two unequal spheres that oscillate in antiphase generating nonlinear steady streaming (SS) flows. We show computationally that the SS flows enable the swimmer to propel itself, and also switch direction as $Re$ increases. We quantify the transition in the swimming direction by collapsing our data on a critical $Re$ and show that the transition in swimming directions corresponds to the reversal of the SS flows. Based on our findings, we propose that SS can be an important physical mechanism for motility at intermediate $Re$.