Investigation of the energy harvesting from the vortex-induced vibration of bluff bodies and the associated dynamic coupling response

This paper experimentally investigated the effects of the cross-sectional shape and attack angle on the vortex-induced vibration of bluff bodies as well as the associated energy harvesting efficiency. The wake flow structures were recognized by using the smoke visualization technology and the numerical simulation. The results indicate that the vibration responses of the triangular, trapezoidal and square cylinders are sensitive to the attack angle. When the vertexes of the triangular and square cylinders and the shorter base of the trapezoidal cylinder are facing the oncoming flow, the vortex shedding presents the 2S mode and the maximum amplitude does not exceed 0.07D. In contrast, the vibration response becomes stronger as the boundary separation points shift to a forward position, when the longer base of the triangular and trapezoidal cylinders and the side of the square cylinder are facing the flow. The response experiences four stages with the reduced velocity increasing: nearly-static, VIV, competition between VIV and galloping, and galloping, respectively. Correspondingly, the phase difference angles between the lift force and cross-flow displacement present four stages: 0°, abruptly jumping from 0° to 180°, switching between 0° and 180°, and dropping to 0°. The associated vortex shedding modes are 2S, 2P, 2P and P + S, respectively. The optimum energy harvesting output with the maximum harvesting efficacy of 12.5% is achieved when the longer base of the triangular faces the flow.