Enhanced performance of airfoil-based piezoelectric energy harvester under coupled flutter and vortex-induced vibration

Abstract

This paper designs a novel airfoil-based flutter piezoelectric energy harvester attached to an unconstrained trailing-edge flap, for transforming the vibration mode and improving the harvesting performance. The flap is first constrained by the flap spring rod and takes place the torsion motion at the smaller angle around the flap shaft. While, when the flap spring rod is removed, the flap is unconstrained, rotates freely, and results in transforming the vibration mode. The mathematical model of fluid-structure-electric coupled fields of the harvester system is first derived, the simulation model of the multi-physical coupled fields is then built, and the wind tunnel experimental setup is finally fabricated. The influence of the flap motions and structural parameters on the flow field, vibration characteristic, and harvesting performance are investigated theoretically, numerically, and experimentally. The results demonstrate that the vibration mode of the harvester system transforms from flutter to vortex-induced vibration at the smaller flap damping coefficients. The flow field verifies that the vortices are shedding at the trailing-edge of the flap and the vibration mode transformation occurs. The unconstrained flap first takes place flutter and then vortex-induced vibration with the increase of the airflow velocity, which enhances the harvesting performance. The unconstrained flap, pitch free play, and the smaller plunge stiffness coefficient decrease the flutter onset of velocity, enhance the aeroelastic vibration and thus improve the harvesting performance. A maximum plunge amplitude of 0.077 m, output voltage of 36.83 V, and output power of 5.43 mW can be harvested for the harvester system “Unconstraint and 1 mm” at 14.39 m/s and 278 N/m. The maximum enhancement ratio of output power for “Unconstraint and 1 mm” is 727.4% higher than that for “Constraint and Zero”. The designed harvester can directly power 14 LEDs and indirectly power a LED for 5 s. This research provides an essential foundation for designing more efficient piezoelectric energy harvesters for promoting actual utilizations in the low-power wireless sensor system.