Stirring by Swimming Bodies

JEAN-LUC THIFFEAULT
University of Wisconsin-Madison

Abstract:
As fish or other bodies move through a fluid, they stir their surroundings. This can be beneficial
to some fish, since the plankton they eat depends on a well-stirred medium to feed on nutrients.
Bacterial colonies also stir their environment, and this is even more crucial to them since at small
scales there is no turbulence to help mixing. We propose a simple model of the stirring action of
moving bodies through both inviscid and viscous fluids. In the dilute limit, this model can be solved
using Taylor's formula for diffusion. We examine the impact on stirring of different behavior of fish
colonies, such as schooling. (This is joint work with Steve Childress.)