Experimental Study on Synchronized Swimming in the Kármán Vortex Behind an Object Using a Fish Robot

It is known that when fish swim in schools, the fish behind can achieve efficient swimming due to the reverse Kármán vortices generated by the fish in front. Theoretical calculations and experimental demonstrations have been conducted on this phenomenon to date. Apart from the tendency of fish to swim in schools, fish in a water flow have a tendency to stay near objects. On the downstream side of an object in a water flow, regions of recirculation (or flow stagnation) occur, and once the water flow exceeds a certain velocity, Kármán vortices are generated downstream. If fish utilize reverse Kármán vortices for efficient swimming, it can be hypothesized that they may also take advantage of the Kármán vortices generated downstream of objects. In this study, we aim to demonstrate this by conducting CFD (Computational Fluid Dynamics) analysis and experiments using a fish robot.