Fluid Elasticity Can Enable Propulsion at Low Reynolds Number

TL;DR

This paper demonstrates that fluid elasticity can enable propulsion at low Reynolds numbers, allowing reciprocal motion to generate movement, which is impossible in purely viscous Newtonian fluids.

Contribution

The study introduces the concept that fluid elasticity can enable propulsion through reciprocal forcing, supported by experimental demonstrations of elastic propulsion with rigid objects.

Findings

Reciprocal actuation can produce propulsion in elastic fluids.

Shape and boundary conditions determine propulsion effectiveness.

Experimental validation of elastic propulsion mechanisms.

Abstract

Conventionally, a microscopic particle that performs a reciprocal stroke cannot move through its environment. This is because at small scales, the response of simple Newtonian fluids is purely viscous and flows are time-reversible. We show that by contrast, fluid elasticity enables propulsion by reciprocal forcing that is otherwise impossible. We present experiments on rigid objects actuated reciprocally in viscous fluids, demonstrating for the first time a purely elastic propulsion set by the object's shape and boundary conditions. We describe two different artificial "swimmers" that experimentally realize this principle.