Enhanced performance of piezoelectric energy harvester incorporating surface protrusions

Piezoelectric energy harvesters can convert ambient vibrations into electrical energy to provide a continuous power source for low-power wireless devices. Inspired by the surface of a dung beetle, this paper proposes an airfoil-based flutter piezoelectric energy harvester featuring surface protrusions to enhance the vibration response and improve the harvesting performance. Three types of surface protrusions, including hemispherical, cylindrical, and triangular prism, are symmetrically attached to the airfoil surface at the position of maximum thickness. The conceptual design of the harvester system is conducted, the wind tunnel experimental setup is constructed, and the experimental prototypes are fabricated. The vibration characteristics and harvesting performance at different surface protrusions, torsional free-play gaps, and airflow velocities are investigated experimentally and numerically. The results show that introducing surface protrusions and torsional free-play nonlinearity effectively improve the harvester's electrical output, low-speed operability, and energy conversion efficiency compared to the baseline design. When the airflow velocity is 7.42 m/s and the torsional free-play gap is 1.1 mm, the harvester system with hemispherical protrusions simultaneously achieves the lowest flutter onset velocity and generates a peak output voltage of 5.53 V, which is 104% higher than that of the baseline of 2.71 V. The variation in torsional free-play introduces nonlinear stiffness in the pitch motion, promoting multimodal coupling and enabling low-velocity oscillations. Combined with the aerodynamic regulation induced by the surface protrusions, these effects enhance strain energy transfer and improve overall energy conversion performance. This work provides a valuable guidance for optimizing airfoil-based flutter piezoelectric energy harvesters using surface protrusion modifications.