Effect of Sea Turtle Flexible Hydrofoil Flexibility and Kinematic Parameters on Hydrodynamic Performance

The patterns of motion of marine organisms provide a new method of propulsion for underwater vehicles, in which flapping foil propulsion is one of the more representative ones. The flexible flapping foil has better propulsion efficiency. The actual flapping foil motion is active and is passively deformed by water. However, numerical simulation is realized by setting up active deformations, making it difficult to accurately reproduce the real deformations. In the study, a pressure tester was used to measure the displacement of the flapping foil to fit the real deformation of the flapping foil, the motion of the sea turtle flapping foil is simplified to the pitching motion in a two-dimensional plane, and its kinematics is modeled. Furthermore, the effects of flexibility as well as kinematic parameters on the propulsive performance of the flapping foil were investigated by means of numerical simulation. The results show that proper flexibility (R = 0.12–0.16) is beneficial to the hydrodynamic performance of flexible foils, but too much flexibility adversely affects the propulsive performance. At a frequency of 1 Hz and an amplitude of 0.075 m, the flexibility that allows the flexible foil to achieve maximum efficiency is equal to 0.13. For the Reynolds number at 35 000 for a flapping foil, the R = 0.06 foil generates more propulsive force than the R = 0.08 foil when the Strouhal number St is smaller than 0.45. Conversely, the opposite is true. The application of these research results to the design of underwater vehicles can provide new ideas for the development of underwater vehicles.