A numerical study of vortex dynamics of flexible wing propulsors

The dynamic properties such as time dependent pressure loading, speed, free stream velocity, and local acceleration of the hydrofoil determine the instantaneous deformation of the hydrofoil, which has effect on the propulsive characteristics of the aquatic animal. A potential flow analysis is done on the flexible hydrofoil, to evaluate the both inertial and elastic effects on propulsive characteristics such as efficiency and thrust coefficient. Thrust coefficient and efficiency are characterised with respect to various non-dimensional parameters such as mass ratio and characteristic frequency for heaving, pitching and combined heave-pitch motions. Results are explained with respect to change in shape of the foil and the dynamics of fluid-structure interaction for various values of mass ratio and characteristic frequency. Thrust coefficient and propulsive efficiency increases with increased mass ratio whereas thrust coefficient and propulsive efficiency increases as characteristic frequency decreases. The flexibility is decreased to a lower value such that the ratio of excitation frequency is equal to the second mode natural frequency and the propulsive parameters are plotted with respect to the flexibility parameter characteristic frequency. It is found that the hydrodynamic output obtained is higher than the hydrodynamic input, thus giving propulsive efficiencies more than one for comparatively low characteristic values. Results of variation propulsive parameters of flexible foil with and without inertial effects with characteristic frequency are presented. There is considerable difference between the propulsive parameters of flexible foil with and without inertial effects.