In developing next-generation autonomous underwater vehicles we look for inspiration from the intelligent designs observed in nature.

For this image, two artificial fish fins are placed side-by-side and flapped in-phase with each another as water flows past the fins (flow direction is up). Small hydrogen bubbles (the white part of the image) allow for the wake of the fins to be visualized. The interaction of the fins creates two repeating patterns of swirling vortices known as vortex streets.