Effect of Flexibility of Caudal Fin on Self-propelled Swimming of Bionic Robot Fish

Based on computational fluid dynamics (CFD) method, swimming of a self-propelled bionic robot fish with 3-DoF was numerically simulated. Swimming performance, thrust of the caudal fin, power consumption of the fish body and leading-edge vortex structure at the caudal fin were compared between the rigid and the flexible caudal fin. The results show that under the same motion parameters, flexible deformation of the caudal fin makes the robot fish swim faster in the acceleration stage, while the rigid caudal fin makes it swimming faster in the cruise stage. Flexible deformation of the caudal fin can reduce fluctuation amplitude of lateral velocity and yaw angular velocity in the cruising stage, which is beneficial to stable swim of the robot fish in a fixed direction. Swimming speed has a negative effect on the flexible caudal fin, but only little effect on the rigid caudal fin. The rigid caudal fin is suitable for robot fish swimming with small lateral translation amplitude of the caudal fin, while the flexible caudal fin is suitable for robot fish swimming with large lateral translation amplitude of the caudal fin. Flexible deformation of the caudal fin can delay the generation and shedding of leading-edge vortexes, so as to result in resistance of the caudal fin in some time duration in one swimming period, which is not conducive to high-speed cruising of the robot fish. © 2022, Editorial Office of Ship Building of China. All right reserved.