A semicircular wall for harvesting wind energy from vortex-induced vibration and galloping

Harvesting energy from ambient air is crucial for sustaining the operation of low-power electronic devices under autonomous conditions. In this study, a specially designed semicircular wall with a thin splitter plate was pro-posed, behind which the wake exhibited evolution from vortex-induced vibration (VIV) to galloping. Benefiting from this peculiar flow pattern, a piezoelectric energy harvester placed in the cylinder wake can perform well under variable wind speed conditions. The effects of aspect ratio (& alpha;) and nondimensional afterbody length (l*) of the semicircular wall on the energy harvester's performance were experimentally examined. The results showed that the aspect ratio was highly correlated with the modes of flow-induced vibrations. When 2/3 & LE; & alpha; & LE; 4/3 and l* = 1/2, the harvester experienced VIV, transition from VIV to galloping, and galloping with a continuously increasing wind speed. Frequency analysis further revealed that the resonance force and lift instability caused by vortex shedding of the semicircular wall might arise almost simultaneously, with the latter serving as the driving factor in the evolution from VIV to galloping. It is also found that the harvester operated efficiently at wind speeds of 1.0-12.0 m/s, and an appropriate nondimensional afterbody length was required to achieve high-level power outputs. These findings provide beneficial suggestions for developing the coupled VIV-galloping energy harvesters.