A hybrid piezoelectric-electromagnetic energy harvester from vortex-induced vibrations in fluid-flow; the influence of boundary condition in tuning the harvester

Abstract

In this paper, a hybrid piezoelectric-electromagnetic energy harvester is proposed to harvest energy from fluid flow around a bluff-body using vortex-induced vibration (VIV). The hybrid piezoelectric-electromagnetic harvester combines the two electromechanical transduction mechanisms through the bluff body excited by VIV: piezoelectric macro-fiber composite and an electromagnetic system. The piezoelectric composite is glued to a substrate beam to convert mechanical strain into electricity. A novel implementation of an internal electromagnetic harvester where the change in magnetic flux inside a coiled holder transduces change in magnetic flux to electricity. An analytical model is used to investigate the narrowband synchronization properties in VIV for different submerged conditions that can be tuned for vibration-based energy harvesting. Under synchronization, the structural natural frequency is the same as the vortex shedding frequency, which leads to the generation of a higher output voltage during frequency matching. Therefore, the effects of added mass and boundary conditions are validated experimentally in water flow to tune the submerged energy harvester with the new hydrodynamic properties to increase the harvesting performance. The results show that fully submerging the energy harvester increases the overall added mass, whilst confining it inside a submerged pipe adds stiffness and damping. This means the overall energy harvesting performance decreases with submerging depth and proximity to the boundary. The maximum voltage output occurs within the synchronization region, with piezoelectric output performing best when partially submerged while the electromagnetic oscillator performs best when fully submerged. Implementing a hybrid piezoelectric-electromagnetic energy harvesting system increased the voltage output by up to 23% compared to a conventional piezoelectric energy harvester.