Abstract: The hydrodynamic characteristics of bionic robotic fish with flexible caudal fin of different shapes were studied. The caudal fin of bionic robotic fish with four shapes has been developed based on the bionic observation results.By conducting hydrodynamic testing experiments,the effects of caudal fin shape,structure,material and motion parameters on hydrodynamic parameters were compared and analyzed. The results indicate that increasing the swing angle and frequency of the caudal fin is beneficial to improve the propulsive performance,but it can also cause instability in swimming;the flexible crescent shaped caudal fin has good propulsion performance;the smaller the aspect ratio,the better the high-frequency swimming performance of the finless caudal fin;the fin ray will reduce the high-frequency swimming performance of the caudal fin.

Key words: flexible caudal fin, multiple shapes, aspect ratio, hydrodynamic characteristics