Enhancing energy harvesting from flow-induced vibration of a semicircular wall via various upstream bluff bodies

Coupling vortex-induced vibration (VIV) and galloping is a promising strategy to enhance the performance of VIV-based piezoelectric wind energy harvesters (PWEHs). In this paper, we proposed to employ upstream bluff bodies to induce the wake of a downstream semicircular wall to evolve from VIV to galloping, where a PWEH was mounted to the semicircular wall. The effects of wind speed, spacing ratio, and cross-section of upstream bluff body on the output performance of the PWEH were examined experimentally. The results showed that an appropriate spacing ratio was required to ensure the occurrence of the wake evolution. Qualitative analyses revealed that the Strouhal number of upstream bluff body could tune the evolving behaviors of the semicircular wall, and the separation distance between VIV and galloping decreased with Strouhal numbers except for the cases in the near wake. The upstream circular and square cylinders performed better in driving the evolution than the trapezoidal and triangular cylinders. The maximum energy conversion efficiency improvement of 38.4% was achieved at a wind speed of 4.0 m/s with a spacing ratio of 10.0 for the upstream square cylinder, compared to that without an upstream bluff body. The findings provide beneficial guidance for developing efficient VIV and galloping coupled energy harvesters.