Experimental Investigation of Hydrokinetic Energy Harvesting From Vortex-Induced Vibration Under Free-Stream Turbulent Flow

Abstract Research into energy extraction from flow-induced vibration has gained momentum owing to the growing demand for clean and sustainable energy. However, studies on the piezoelectric energy harvesting from the vortex-induced vibration (VIV) in water remain limited. This study experimentally investigates the hydrokinetic energy harvesting from a two-degree-of-freedom VIV of a flexibly mounted circular cylinder under free-stream turbulent flows that could mimic actual sea environments. The experimental setup consists of a cylinder mounted vertically on a leaf-spring elastic base system in Newcastle University’s water flume, where repeatable incoming turbulent flows are generated with a maximum flow turbulence intensity of about 14%. The system has unequal two-dimensional mass ratios of 3.14 (X) and 1.88 (Y), while achieving comparable natural frequencies of 0.6 (X) and 0.67 Hz (Y). The experiment operates at a maximum reduced velocity of 15 and Reynolds number of about 9,000. The cylinder in-line (X) and cross-flow (Y) responses are captured using accelerometers. Piezoelectric patches are attached to the flexible leaf-plates, outputting electrical power. The effect of load resistance is studied. Dynamic responses exhibit typical VIV characteristics, including initial, upper and lower branches, intermittent amplitude shifts between upper and lower branches, and dual 2:1 (X:Y) resonant frequencies resulting in figure-8 shaped, modulated trajectories. A trend in the power generation qualitatively follows the response features, with a maximum power output in the level of microwatts at peak amplitudes. Voltage trajectories display modulated two lobes with irregular shapes, signifying the influence of free-steam turbulence on the flexing of elastic leaf-plates. These fundamental insights would be useful for developing VIV-based energy harvesting devices in actual ocean environments with turbulence. The consideration of in-line VIV alongside cross-flow VIV for energy harvesting is also novel, potentially enhancing the overall power output and enlarging parametric ranges for sustainable energy solutions.