Numerical simulation of a self-propelled fish-like swimmer with rigid and flexible caudal fins

Aim: In this paper, numerical simulations were conducted to investigate the swimming performances, hydrodynamics performances and wake structures of a self-propelled swimmer with rigid and flexible caudal fins.Methodology: The kinematics model of the swimmer was constructed using thunniform swimming. Using computational fluid dynamics (CFD) method, the systematic study of swimmer with rigid and flexible caudal fins was carried out. Results: The results showed that the caudal fin flexibility is beneficial to the fast-start of fish but not conducive to the fast cruising of fish. The fish with rigid caudal fin has larger cruising velocity inquasi-steady swimming and smaller forward acceleration in fast-start stage. In addition, the caudal fin flexibility is also beneficial to the heading stability of fish’s self-propelled swimming. The pressure distribution on the fish surface indicates that most of the thrust is generated by the leading-edge region of the caudal fin. The visualization of wake structures showed the existence of the attached leading-edge vortex (LEV) in thunniform swimming. Interpretation: Based on the present simulations, the hydrodynamic performance of tuna during self-propelled swimming was analyzed in detail. Researchers can use these findings to design bionic robot fish with rigid and flexible tails.