Ultra-low-cut-in galloping of a reverse-C-with-tail piezoelectric harvester for low-speed wind energy conversion

Galloping-based piezoelectric harvesters are promising for weak-wind energy conversion, but many existing designs still require a relatively high cut-in wind speed. This study proposes a reverse-C-with-tail bluff-body harvester to address this limitation. Preliminary fixed-body CFD results show stronger lift-coefficient fluctuations for the tailed geometry, while the pressure contours and streamlines qualitatively suggest a more extended recirculating-flow pattern and a more pronounced upper–lower pressure contrast. Wind tunnel experiments show a repeatable voltage-response-based cut-in at approximately 1 m/s. As the wind speed increases, the response becomes galloping-dominated. The S5 configuration reaches 46.4 V and a fixed-load power output of 2.152 mW at 7 m/s under RL = 1 MΩ, outperforming the tailless baseline. Further tests indicate that tail length is the primary geometric factor governing the reduction in the voltage-response-based cut-in wind speed and the subsequent output growth, while curved-section thickness provides secondary refinement. After A1 and A3 were fitted to the measured RMS-voltage data, the reduced-order electromechanical model reproduced the main voltage trends and provided an interpretive framework for the geometry-dependent response. These results establish the proposed configuration as an ultra-low-cut-in design strategy for galloping-based piezoelectric energy harvesting.