Effects of different paddling motion patterns and flexibility on hydrofoil propulsion performance

A bi-directional fluid-solid interaction method is used to simulate the "8" shape motion of the hydrofoil of a bionic penguin. The feasibility of the numerical simulation method is verified by building an experimental platform. The effects of the forward and backward paddling motion (no front and back F0, symmetrical F1, and asymmetrical F2) and the flexibility (high, medium, and low flexibility intervals) on the propulsion performance are considered. The results show that the best propulsion performance is obtained in the medium and low flexibility ranges for F0 and F1 and the medium flexibility range for F2. At the same flexibility, F0 achieves the best propulsive efficiency but the lowest average and peak instantaneous thrust coefficients, and as the amplitude of motion increases, the propulsive efficiency decreases and the average and peak instantaneous thrust co-efficients increase; for similar input power, F2 can achieve higher peak instantaneous thrust coefficients. The vortex and pressure fields under different parameters are analyzed through post-processing further to explain the reasons for the differences in propulsion performance. The findings of the study are of great significance for the unraveling of the hydrofoil propulsion mechanism and the optimal design of future hydrofoil propulsion systems.