Locomotion of helical bodies in viscoelastic fluids: enhanced swimming at large helical amplitudes

TL;DR

This study investigates how viscoelastic fluids influence the swimming behavior of helical bodies, revealing that large-amplitude helices can experience enhanced propulsion depending on fluid and geometric parameters.

Contribution

It provides numerical analysis of helical swimming in viscoelastic fluids, demonstrating the breakdown of previous theories at large amplitudes and identifying conditions for speed enhancement.

Findings

Large pitch angle helices achieve maximum speed at Deborah number ~1

Viscoelasticity can both enhance and retard swimming speed

Numerical results connect small-amplitude theory with large-amplitude experiments

Abstract

The motion of a rotating helical body in a viscoelastic fluid is considered. In the case of force-free swimming, the introduction of viscoelasticity can either enhance or retard the swimming speed and locomotive efficiency, depending on the body geometry, fluid properties, and the body rotation rate. Numerical solutions of the Oldroyd-B equations show how previous theoretical predictions break down with increasing helical radius or with decreasing filament thickness. Helices of large pitch angle show an increase in swimming speed to a local maximum at a Deborah number of order unity. The numerical results show how the small-amplitude theoretical calculations connect smoothly to the large-amplitude experimental measurements.