Numerical simulation on the interaction of median fins for enhancing vortex dynamics and propulsion performance in fish self-propelled swimming.

This article investigates the hydrodynamic effects of interactions among median fins—the dorsal, anal, and caudal fins—on the self-propelled swimming performance of grass carp, a semi-migratory fish species. Using three-dimensional numerical simulations based on a high-precision scanned model of grass carp, the study compares swimming speed, thrust, drag, and propulsion efficiency across different fin movement scenarios. Results show that coordinated movements of the median fins can increase average swimming speed by up to 4.6 times, thrust by 33.47%, and swimming efficiency by 25.48% compared to swimming with only the trunk and caudal fin. The enhancement is attributed to the formation of strong posterior body vortices generated by the dorsal and anal fins, which are captured by the leading edge of the caudal fin, intensifying the leading-edge vortex and thus increasing thrust. These findings elucidate the vortex dynamics underlying median fin interactions and provide insights into the efficient propulsion mechanisms of fish swimming in nature.