Performance analysis of flapping-foil energy harvesters under shear-flow conditions

Flapping-foil energy harvesters represent a promising technology for extracting energy from fluid flows, although their performance under shear-flow conditions is poorly understood. To address this research gap, we investigated the impact of power-law shear flow on the performance of flapping-foil energy harvesters. We conducted numerical simulations at different Reynolds numbers (Re = 1000, 50 000, and 500 000) under uniform-flow and shear-flow conditions. Based on the results, shear flow minimally affected the power outputs at Re = 1000 and 50 000, where viscous forces dominate the flow dynamics. However, at Re = 500 000, shear flow significantly reduced the power output, by up to 10% relative to uniform flow, primarily due to alterations in the vortex shedding and pressure distributions resulting from the velocity gradient. Additionally, we considered variations in the heaving amplitude and found that although this parameter has minimal effect at low Reynolds numbers, it is critical at Re = 500 000. Specifically, the performance disparity between uniform and shear flows was pronounced at low amplitudes. These findings highlight the importance of considering shear-flow effects and optimizing the heaving amplitude to maximize the performance of flapping-foil energy harvesters in realistic fluid environments.