The time asymmetric pitching effects on the energy extraction performance of a semi-active flapping wing power generator

Inspired from the bird and insect's flight in nature, the time asymmetric pitching motion is proposed for the semi-active flapping wing power generator instead of conventional time symmetric pitching motion to seek better energy extraction performance. The NACA0012 wing, with prescribed pitching motion, is employed to represent as a power generator, where the vertical hydrodynamic force activates its heaving motion. A novel numerical coupling model is developed to simulate the interaction between the fluid and the semi-active power generator, and the effects of time asymmetric pitching on the energy extraction performance of the generator is analyzed. It is found that the time asymmetric pitching motion has a noticeable effect on the energy extraction performance of the generator, as it affects the instantaneous energy coefficient, energy efficiency and the flow structures. It is also concluded that with an optimal time asymmetric pitching motion, the maximal efficiency increases as high as 17% over the time symmetric pitching power generator.