Hydrodynamics study of dolphin's self-yaw motion realized by spanwise flexibility of caudal fin

The hydrodynamic performance of the virtual underwater vehicle under self-yaw is investigated numerically in this paper, we aim to explore the fluid laws behind this plane motion achieved by the bionic flexibility, especially the spanwise flexibility of the caudal fin. The kinematics of the chordwise flexible body and the spanwise flexible caudal fin are explored through dynamic mesh technology and user-defined functions (UDF). The 3-D Navier-Stokes equations are applied to simulate the viscid fluid surrounding the bionic dolphin. The study focuses on quantitative problems about the fluid dynamics behind the specific motion law, including speed of movement, energy loss and working efficiency. The current results show that the self-yaw can be composed of two motions, autonomous propulsion and active steering. In addition, the degree of the flexible caudal fin can produce different yaw effects. The chordwise phase difference Ф is dominant in the propulsion function, while the spanwise phase difference δ has a more noticeable effect on the steering function. The pressure distribution on the surface of the dolphin and the wake vortex generated in the flow field reasonably reveal the evolution of self-yaw. It properly turns out that the dolphin can combine the spanwise flexible caudal fin and the chordwise flexible body to achieve self-yaw motion.