Efficiently harvesting low-speed wind energy by a novel bi-stable piezoelectric energy harvester from vortex-induced vibration and galloping

Designing low-cost and simple harvesters to convert natural wind energy into electricity is regarded as a promising method to realize the self-powering of node sensors in the Internet of Things. However, the inherent challenge lies in the typically low and fluctuating speeds of environmental wind, making efficient energy harvesting a difficult task. To address this challenge, this study introduces a novel bi-stable wind energy harvester designed to undergo interwell oscillations through the synergistic effects of vortex-induced vibration and galloping. The bi-stability is achieved by incorporating three magnets. To enhance the extraction of energy from low-speed wind, a square-sectioned bluff body is affixed to the cantilever beam's tip, accompanied by two foam balls. Simulations elucidate the fluid dynamics around the bluff body and foam balls, revealing that the induced vortex causes swinging in the balls, subsequently driving the piezoelectric beam to oscillate and jump. The study establishes the potential energy and force-displacement relationship of the proposed harvester to provide insights into the flow fields. A physical prototype of the harvester is fabricated and subjected to verification experiments in a wind tunnel. Results indicate that the proposed harvester exhibits snap-through or inter-well oscillations, generating a desirable energy output at wind speeds exceeding 1.3 m/s. Notably, even at very low wind speeds, the proposed harvester, despite exhibiting the same intra-well motion as its linear counterpart, achieves significantly higher output voltage due to magnetic interaction and bi-stability. Demonstrating superior performance with a voltage output of up to 10.5 V at a wind speed of 1.6 m/s, compared to the mere 0.7 V from its linear counterpart, the proposed harvester shows the advantages of bi-stability and snap-through motion in low-speed wind energy harvesting.