Energy harvesting from water flow in open channel with macro fiber composite

Abstract

Fluid-induced vibrational energy harvesting usually concerns small-scale wind energy extraction. A few efforts have been made into energy harnessing from low-velocity water flows. In this study, low-speed galloping and vortex induced vibration (VIV) are investigated for energy harvesting in an open channel via the macro fiber composite glued on the surface of a cantilever beam. A cylindrical or triangular-prism bluff body is attached at the free tip of the beam and fully immersed in the water. Beam’s deflection is perpendicular to the fluid flow. The flowrate of the water channel is measured by a built-in rectangular sharp-crested weir, and the average flow velocity is controlled by the inlet valve and weir plate. The fluid-structure interaction and electromechanical coupling at different flow velocities and load resistances are analyzed. At small flow velocities, the cylindrical bluff body exhibits better performance than the triangular-prism bluff body since it has been shown in previous work [So et al., J. Fluid Struct. 24, 481–495 (2008) and Daniels et al., J. Wind Eng. Ind. Aerod. 153, 13–25 (2016)] that for the same turbulence intensity the cylinder under VIV performs better than the triangular prism. As the flow velocity increases, the power of the triangular-prism case harvested from the interaction of low-speed galloping and VIV overtakes the power of the cylindrical case converted from the VIV motion that is usually smaller than the cylinder diameter. One dominant vibration frequency is noticed and associated with lock-in or wake capture, which increases with the flow velocity owing to the decreasing added mass. High efficient energy harvesting from the low-velocity water flow is realized via the integration of galloping and VIV.