Abstract: A comprehensive study was presented on the effects of the caudal fin shape on the propulsion performance of a harmonically heaving and pitching caudal fin. A biocaudal fin propulsion mechanics was designed and a series of hydrodynamic experiments for three caudal fin shapes (the whale caudal fin, the dolphin caudal fin, and the tuna caudal fin) were performed. Then numerical simulations were done. Both the experimental and computational results indicate that the tuna caudal fin produces the highest efficiency, although the mean thrust coefficient and input power coefficient of the tuna caudal fin was the smallest. The characteristics of wake were analyzed to find that not only the wake scale of the tuna caudal fin is the smallest, but also the vorticity magnitude of the tuna caudal fin is the weakest.

Key words: flapping caudal fin, caudal fin shape, propulsion performance, wake