Effects of Motion Parameters on the Propulsion and Energy Harvesting Performance of a Wave-Driven-Heaving Flapping Foil

Abstract

The propulsion and energy harvesting performances of a flapping foil have been investigated base on immersed boundary method. The heaving and pitching motions are respectively driven by the wave and the external actuator. The effects of phase difference and frequency difference between the pitching and heaving motion as well as the nonharmonic pitching motions on the propulsion and energy harvesting performances were studied at the Re=1100. For the small pitching amplitude of 30°, the upstream propulsion is the highest when the phase difference is 270°, and the nonharmonic motion is ineffective for enhancing propulsion. For the large pitching amplitude of 76.3°, the downstream propulsion and energy harvesting efficiency are the highest when the phase difference is 247.5°. The optimum frequency difference is zero, i.e. the pitching frequency is equal to the wave frequency. Meanwhile, the nonharmonic motion is helpful for improving the propulsion and the energy harvesting efficiency. The downstream propulsion is increasing with the increase of nonharmonic parameter of β. The maximum time-averaged pure output power coefficient of 1.09 is obtained at β=1.85. But the highest energy harvesting efficiency of 45.58% is obtained at β=1.15.