Abstract:Fish has been the important study object of biologists and bionics researchers for a long time for their efficient and flexible swimming ability. This paper selects the fish in the swimming mode of caudal fin propulsion as the study object, and the geometric model and motion control model of biomimetic fish were constructed. The Computational Fluid Dynamics (CFD) method together with dynamic grid technology was used to simulate their swimming behavior numerically and analyze the propulsion mechanism of the caudal fin swing. On this basis, by changing the parameters such as the tail beat frequency, swing amplitude, body wave length and body shape, combined with biological characteristics such as fish's dash movement, swimming style and body shape evolution, the influence on the swimming ability of fish under different parameters was explored.The results show that the reverse Kármán vortex street generated in the tail flow field when they move is the main cause of the propulsion force. With the increase of tail beat frequency and swing amplitude, fish can get a higher dash speed in a short time. When λ=0.75 L, a(x)max=0.1, in order to obtain the swimming speed of 1.0 L/s, the tail beat frequency should reach about 2 Hz. The change of body wave length (λ) will change their swimming mode. When the wave length reaches about 0.75 L, the fish can swim forward at a speed of 0.5 L/s, and the propulsion increases with the increase of body wave length. Compared with fish with large head and small body, fish with slender body have less pressure difference resistance when swimming, so they can obtain greater thrust in the same caudal fin propulsion mode. The research results of this paper can provide some reference for the optimization design of the bionic underwater vehicle.