Abstract: In order to improve the hydrodynamic performance and energy harvesting efficiency of the oscillating hydrofoil, an improved motion model was proposed based on the traditional simple harmonic motion model. By introducing the pitch motion coefficient k, the general form of the improved pitch motion law was deduced. The two-dimensional model of the hydrofoil was established using Fluent software, and we further analyzed the effects of different pitch motion coefficients, motion frequency and pitch amplitude on the hydrofoil energy capture performance under the semi-active oscillation model. The results showed that, when compared with the traditional simple harmonic motion model, the improved motion model could make the lift coefficient of hydrofoil maintain a larger value for a longer period of time, meanwhile the lift coefficient and energy capture efficiency of the hydrofoil also were improved. Under the same value of reduced frequency and pitch amplitude, reducing the pitch motion coefficient could increase the angular velocity of the pitch angle rotation, thereby increasing the energy consumed by the pitch motion. Different pitch amplitude corresponded to different optimal reduced frequencies. The lower the reduced frequency, the more unstable energy-capturing performance of the hydrofoil, the greater the pitch amplitude, and the more energy consumed for turning the pitch angle. Under the given parameters, the energy conversion efficiency of the hydrofoil could exceed 40%.

Key words: oscillating hydrofoil, improved motion model, pitch motion coefficient, hydrodynamic characteristic, energy-capturing efficiency