Effects of hydrofoil motion parameters and swing arm parameters on power extraction of a flexible hydrofoil in swing arm mode

Abstract

This study aimed to numerically investigate the power extraction performance of an oscillating hydrofoil with a time-varying camber in the swing arm mode. The effects of the swing arm length (R), swing arm amplitude (H0), pitching amplitude (θ0), reduced frequency (f*), and flexure amplitude (α) on the average power coefficient (CP‾) and efficiency (η) were investigated. The results revealed that, with an increase in α, the force coefficients were improved, which is beneficial for improving the power extraction capability. At α = 15%, η of the flexible hydrofoil was 38.5%; this represents an increase of approximately 40.5%, as compared to rigid hydrofoils. Further, R and H0 of the swing arm caused variations in the vertical amplitude of hydrofoils, thereby altering the motion velocity and effective angle of attack and further affecting the evolutions of the flow fields and vortices, pressure distribution, and force coefficients. Moreover, the leading-edge vortex was found to separate from the hydrofoils gradually in advance with an increase in θ0, whereas the increase in f* decreased the synchronization between the directions of the force coefficient and motion velocity. Furthermore, it was found that the optimal f*, which could reach peak values of CP‾ and η, increased with θ0.