Bistable dual cantilever flutter for potential wind energy harvesting applications

Abstract

This paper examines the potential of bistable dual cantilever flutter (DCF) for wind energy harvesting applications. Two cantilever beams were placed side by side and perpendicular to the direction of the wind flow to create a unique phenomenon known as the DCF. Similar pole magnets were then attached to the free end of each beam to establish a bistable condition. A theoretical model was presented and was shown to agree well with the experimental measurement. The mass of the magnets caused the frequency of the beams to drop by approximately 4.5 times compared to the monostable DCF. When the two beams were placed 21.0 mm apart, the bistable beams achieved a stable state at a critical flutter speed of 5.3 ms−1 and displayed significantly large, anti-phase oscillations that is approximately three times larger than the monostable DCF. Further increase in this distance showed a decreasing trend with the critical flutter speed, which opposes the expected trend of the monostable DCF. Due to the bistable effect, significant flutter amplitudes were also obtained during a backward sweep when the wind speeds were incrementally reduced from high to low, recording a 73.2 % increase in bandwidth for one of the tested cases. This suggests the possibility of an ultra-wide bandwidth energy harvester. Finally, it was shown that the piezoelectric conversion method is more favourable for the bistable DCF whereas electromagnetic induction is preferred for the monostable DCF.