Design and characteristic analysis of a piezoelectric-electromagnetic hybrid energy harvester undergoing a VIV-galloping transition via the combined bluff body with flexible membrane wing

The significant potential of flow-induced vibration energy harvesters in meeting the power supply demands of sensor network nodes has attracted extensive research. To provide a feasible solution for the limitations of weak output performance and poor reliability of most existing piezoelectric-electromagnetic hybrid energy harvesters at high wind speeds, a novel design enabling a transition between vortex-induced vibration and galloping through an adaptive flexible-membrane bluff body is proposed in this paper. Unlike conventional harvesters relying on rigid bluff bodies, a combined bluff body composed of a flexible membrane and a cylinder is introduced, where it can dynamically adapt to the wind speed. This design can amplify vibration response under low wind-speed conditions while suppressing excessive oscillations at high airflow velocity. Also, it employs a hybrid energy conversion mechanism to markedly boost both output performance and operational reliability. A theoretical modelling of the harvester is conducted and validated through computational fluid dynamics simulations and experimental testing. The results indicate that, by tuning the structural parameters of the combined bluff body, the harvester can be modulated to diverse operating conditions, achieving a minimum cut-in wind speed of 1.4 m/s. And, a peak piezoelectric output of 92.5 V and a peak electromagnetic output of 13.5 V can be obtained. Also, under a width-diameter ratio α = 1.5 and thickness ratio β = 1 with the wind speed of 11 m/s, a single piezoelectric vibrator and electromagnetic coil generate output powers of 1.18 mW and 5.04 mW, respectively. Furthermore, they can individually illuminate 50 and 180 blue LEDs at v = 5 m/s. In practical demonstrations, the harvester can successfully power 8 lamp beads and maintain continuous proper operation of a digital thermometer.