Effect of pectoral fin locomotion parameters on fish propulsive performance

Abstract To investigate the influence of pectoral fins on the propulsive performance of fish, a numerical simulation method was employed to systematically analyze the effects of flapping frequency and amplitude on swimming performance. The fish body and pectoral fins were modeled using a NACA0012 airfoil and rigid flat plates, respectively. Self-propulsion of the fish body in a quiescent flow field was achieved through a user-defined fin motion function. The results indicate that as the flapping frequency increases from 1 Hz to 5 Hz, the average cruising speed of the fish increases by approximately 733%, while the propulsive efficiency decreases by about 54%. When the flapping amplitude increases from 30° to 50°, the average cruising speed and propulsive efficiency increase by approximately 179% and 42%, respectively. Under low-speed and long-distance cruising conditions, a smaller amplitude yields higher energy efficiency. Visualization of the vorticity and pressure fields reveals that high-frequency and large-amplitude fin motions significantly enhance the vortex structures in the fin wake, increase the pressure difference between the anterior and posterior regions of the body, and consequently improve thrust and swimming speed. Furthermore, asymmetric flapping of the left and right fins generates lateral moments, inducing body rolling and yawing, which facilitate postural adjustment and turning in disturbed flow environments.