Hydrodynamic piezoelectric energy harvesting with topological strong vortex by forced separation

Abstract

Inspired by the fish tail, we propose a piezoelectric energy harvester based on flow induced vibration with topological strong vortex by forced separation for low-velocity water flow. Observed using computational fluid dynamics, the high surface curvature at the up and down edges of the elliptic cylinder forces the boundary layer to separate and forms strong vortex squeezed on the bluff body. The extended Hamilton’s principle is used to derive the governing equation of the electromechanical coupling system and the Galerkin procedure is introduced to calculate the analytical output of the energy harvester. An experimental study with macro fiber composite in a circulating open U-shaped channel is conducted. The output voltage for the elliptic cylinder with an aspect ratio of 2.5 under the water velocity of 0.45 m/s is 38.4 V, 21.5 times higher than that for the circular cylinder. The hydrodynamic negative and positive damping determined by the shape of the bluff body balance the energy pumped in and dissipated in a period and fix its phase portraits at a stable limit cycle, resulting in the self-excited vibration of the bluff body. Optimal resistance analysis shows that changing parameters of the bluff body such as reducing its mass or increasing its length also improves the energy harvesting efficiency. The results are helpful for the optimal design of energy harvesters at low water velocity.