Simulations and experiments on a hydrodynamic compound pendulum piezoelectric energy harvester accompanied with vortex-induced vibration

A compound pendulum piezoelectric energy harvester (CPPEH) accompanied with vortex-induced vibration (VIV) was proposed to convert the water flow energy to electricity. The harvester was composed of a piezoelectric cantilever beam and a parallel cylinder, which has the advantages of exempting from encapsulation insulation, greater vibration response and being easy to generate vortex-induced resonance in low-speed water flow. The effects of water velocity on the hydrodynamic response and energy harvesting performance of the CPPEH were investigated by virtue of the simulation analysis on the fluid-structure-electric coupling and experimental tests. It is found that the output power first increases as the load resistance increases, the maximum power output is obtained when reaching the optimal resistance, and then the output power decreases. The vibration amplitude and output power have the same changing relation with the flow velocity and the maximum power output is obtained at the vortex-induced resonance. The vibration frequency is overall increasing with the increase of the flow velocity. However, because of the “lock-in” of the vortex-induced vibration, the vibration frequency is mainly equal to the natural frequency of the CPPEH during the vortex-induced resonance. The output power of the harvester is enhanced with the increase of cylinder diameter, while the vibration velocity of the vortex-induced resonance is increased at the same time.