Role of Shape and Kinematics in the Hydrodynamics of a Fish-like Oscillating Hydrofoil

In the present two-dimensional numerical study, we investigate the roles of geometrical parameters of a hydrofoil (shape/curvature of the leading and trailing edges and thickness) and kinematic parameters (phase difference between heave and pitch (phi)) on the propulsive performance of different-shaped hydrofoils oscillating at maximum angles of attack up to alpha max=30 circle. The study was carried out at a fixed non-dimensional maximum heave to chord ratio h circle/C=0.75, Strouhal number St=0.25, and Reynolds number Re=5000. Our findings reveal that hydrofoil performance and stability improve with leading and trailing edge curvatures but decline as thickness increases. By analyzing the near-wake structure, we establish that even minimal flow separation increases power consumption while moderate flow separation enhances thrust. Over the range of different-shaped hydrofoils at different alpha max and phi, maximum propulsion efficiency occurs for those parameters for which there is a small degree of flow separation but with no roll-up of a separating vortex. In comparison, maximum thrust generation occurs when there is a moderately strong flow separation but without induction of a significant amount of fluid around the trailing edge. These insights offer valuable knowledge for understanding fish propulsion efficiency and have applications in designing autonomous underwater vehicles (AUVs) and micro-air vehicles (MAVs).

Automated summary

In this study, the effects of geometrical and kinematic parameters on the propulsive performance of hydrofoils were investigated. The results show that leading and trailing edge curvatures improve hydrofoil performance and stability, while increasing thickness decreases performance. The optimal conditions for maximum propulsion efficiency involve minimal flow separation without a separating vortex, while maximum thrust generation occurs with moderate flow separation without significant fluid induction around the trailing edge. These findings provide valuable insights for understanding fish propulsion efficiency and have practical applications in the design of autonomous underwater vehicles and micro-air vehicles.