A study of a flapping flag in viscoelastic fluids and its implications for micro-scale swimming in biofluids

Abstract

Biological cells and organisms employ a different method of propulsion when in viscous, viscolelastic fluids rather than Newtonian fluids. By studying the dynamics of a flag under a flow of a viscoelastic fluid, we hope to better understand the swimming dynamics in these biological fluids. A slender polysiloxane rod was placed in a rotating annulus filled with a cetyl pyridnium chloride micellar solution and also with a xanthan gum solution. Flapping of the rod was observed with the micellar solution for Weissenberg numbers greater than 1, where elastic forces in the fluid dominated the elastic force in the flag. Flapping was not observed in the xanthan gum for Weissenberg numbers up to 250, where the elastic force in the flag dominated the elastic force in the fluid. The observation of a flapping flag in a viscoelastic fluid indicates that, unlike in a Newtonian fluid, the polymers in the fluid can interact with an elastic body to cause a flapping motion which may indicate why the swimming dynamics of sperm change with their fluid environment.