Physics (Internal)

Sailing on Diffusion

This event is part of the Physics Department Colloquia Series.

Buoyancy-driven flow, which is flow driven by spatial variations in fluid density, lies at the heart of a variety of physical processes, including mineral transport in rocks, the melting of icebergs and the migration of tectonic plates. Here, we report on a new discovery that buoyancy-driven flows can also generate propulsion. Specifically, we find that when an asymmetric object floats in a density-stratified fluid, the diffusion-driven flow at its sloping boundaries draws energy and momentum from microscale molecular diffusion to produce a macroscopic sideways thrust. This remarkable and fundamental discovery has implications for transport processes in regions of varying fluid density, such as the ocean pycnocline, and wherever there is a temperature difference between immersed objects and the surrounding fluid.