Effect of spanwise deformation on the energy harvesting performance of a semi-active hydrofoil

This study, based on three-dimensional numerical simulations, systematically investigates the effects of the phase difference φ_p and the Strouhal number St on the energy harvesting performance of a semi-active flapping hydrofoil under spanwise deformation conditions. By analyzing the evolution characteristics of the vortex structures under different operating conditions, the underlying hydrodynamic mechanisms are revealed. Within the range of the maximum bending angle ψ_max = 0-25°, simulations of the flapping process were conducted for a NACA0015 hydrofoil with an aspect ratio of 4. The results show that spanwise deformation exhibits a significant phase dependence on the energy harvesting performance: deformation suppresses the output power within the range of φ_p = 0-315°, while it enhances the output power in the remaining phase difference ranges. The maximum increase in the mean output power coefficient exceeds 29% at φ_p = 270°. In addition, under the condition of φ_p = 0, when St = 0.15 and 0.2, the output power increases with the increase of ψ_max. Flow field analysis indicates that appropriate spanwise deformation can regulate the stability of the leading-edge shear layer, modify the development characteristics of the leading-edge vortex (LEV), and enhance the strength of the tip vortex (TV), thereby optimizing the lift distribution on the hydrofoil surface and improving the energy harvesting performance. This study provides a theoretical reference for efficient energy harvesting of semi-active flapping hydrofoils under spanwise deformation conditions.