Enhancing power generation in steel flag-based flutter energy harvesters

Abstract

This study aims to identify the effective combination of design parameters to maximize the power generation from flexible steel flag-based flutter energy harvesters. Ambient wind energy is captured from self-sustained oscillations beyond the flutter onset speed, wherein bending oscillations of the flag beam are converted into electrical energy through a piezoelectric coupling using macro-fiber composites. The experiments are performed by varying key parameters like piezoelectric active area, external load resistance, flow speed, and flag shape to determine the most effective configuration for power generation. The dynamic response of the piezoelectric flag exhibits a subcritical bifurcation route. The average output power increases gradually with the flow speed. Increasing the active area from 392 mm${}^2$ to 595 mm${}^2$ leads to nearly 20-fold amplification in generated power, whereas a further doubling of the active area yields only a marginal gain. Among multiple piezoelectric flags with active areas between 392–1190 mm${}^2$, the one with 595 mm${}^2$ performs best with highest power density of 0.588 $\mu$W/mm${}^3$, along with the broadest flow regime for energy harvesting. The peak output power is achieved for external load resistances between 0.1 and 0.27 M$\Omega$. Among the tested flag geometries (triangular, square, trapezoidal, and rectangular), the triangular shape performs best with the lowest flutter speed and highest harvested power. Average output power up to 62–66 $\mu$W can be achieved within the 6–10 m/s flow speed range from the proposed energy harvester, suitable for operating low-power wireless sensors.