Low velocity water flow energy harvesting using vortex induced vibration and galloping

Abstract

The oceans, seas, rivers and channels store abundant renewable low velocity flow energy but without large-scale exploitation. For energy harvesting, the vortex induced vibration (VIV) and galloping convert flow energy to vibration energy. This paper studies the piezoelectric energy harvesting from low velocity water flow by VIV and galloping. A piecewise distributed parameter model for the piezoelectric cantilever beam with three types of bluff bodies is proposed. The modified Van der Pol model is established to simulate the VIV force for the cylinder bluff body, and the quasi-steady hypothesis is used to obtain the galloping hydrodynamic force for the tri-prism and semi-cylinder bluff bodies. The added-mass term of the hydrodynamic force is accounted in both the VIV and galloping forces. The approximate analytical solutions of the harvested power for the VIV and galloping models are derived. The circulating water channel experiments are performed and verify the theoretical models. The harvested maximum power density is 1.949 mW/cm3 for the VIV harvester at the flow velocity of 0.48 m/s. The harvested maximum power densities are 4.286 mW/cm3 and 7.582 mW/cm3, respectively for the tri-prism galloping harvester and semi-cylinder galloping harvester at the flow velocity of 0.54 m/s. The fluid fields for the three bluff bodies are simulated using the large eddy simulation turbulence model to present the vortex, pressure and velocity distributions. This study indicates that the galloping energy harvesting is superior to the VIV energy harvesting. The ratio of the linear to the cubic hydrodynamic coefficient is crucial in the galloping energy harvesting.