Flow-energy harvesting using a fully passive flapping foil: A guideline on design and operation

Following our previous work [Int. J. Mech. Sci. (2020), vol. 177, 105587], we searched the best power extraction performance of a novel flow-energy harvester, which utilizes a fully passive flapping foil to extract energy from air/water flows. A series of water-tunnel experiments were conducted on the same test model at the Reynolds number around 10(5). Through investigating the effects of two unexplored key parameters, a higher overall maximum power conversion efficiency of 42. 7% was obtained at water speed 0.71 m/s and foil pitching amplitude 60 degrees, corresponding to a larger mean power output of about 1.51 W. A quasi-steady theoretical model was also developed to fast predict the system performance in a larger parameter space. It was found that, in addition to typical dynamics, i.e., a flapping cycle includes two pure-heaving phases and two stroke-reversal phases, the foil system can also continuously operate in a no-pure-heaving zone where a flapping cycle only includes two successive stroke-reversal phases. Through these experimental and theoretical studies, a useful guideline was proposed on the design and operation of the foil system.

Automated summary

This study investigates a novel flow-energy harvester utilizing a passive flapping foil to extract energy from air/water flows. Through water-tunnel experiments and a theoretical model, the optimal power conversion efficiency and mean power output were obtained by studying two key parameters. A useful guideline for the design and operation of the foil system was proposed based on these experimental and theoretical studies.