Thrust enhancement by traveling wave-based surface-undulation on a pitching hydrofoil

A fluid-structure interaction study is conducted on a pitching hydrofoil with traveling wave-based surface undulations at Re=5000, using an in-house developed solver based on immersed interface method with a level-set to define the interface. We extend our previous work (Shukla et al., 2022) and analyze the combined effect of surface-undulation on the propulsive performance of a pitching hydrofoil. We consider a constant pitching amplitude, local thickness to amplitude ratio, and wave number of surface-undulation. The phase speed of surface-undulation and pitching frequency has been varied. The combined motion increases thrust and promotes the asymmetry in the vortex street even at a lower pitching Strouhal number. Thrust generation is due to the combined effect of the pressure-suction mechanism on the surface of the hydrofoil and the formation of reverse von-Karman vortices behind the hydrofoil. Flow regime maps show that the maximum efficiency occurs in the pitching-dominated region and the region of the asymmetric wake. In contrast, the maximum thrust is found in the surface-undulation-dominated and deflected asymmetric wake regions. The propulsive performance of combined motion increases compared to the purely pitching motion.