Energy harvesting from wake-induced vibration of flexible flapper behind a bluff body

Piezoelectric energy harvesting from ambient vibrations offers a promising small-scale energy generation strategy, with wake-induced vibration of flexible structures being an ideal candidate. This study examines a bluff body followed by a fully flexible piezoelectric flapper in a viscous free-stream flow using an in-house discrete forcing immersed boundary method-based fluid-structure-electric energy solver for parametric investigation. Different vortex shedding regimes are identified based on vortex formation around the flexible flapper. The complex and interdependent spatiotemporal dynamics of the wake and flexible body dictated by parameters such as bending rigidity and the gap space between the flapper and bluff body result in various deformation profiles, influencing the strain rate and output power. The study also investigates the independent variation of flapper length and its impact on vortical arrangements and flexibility, introducing different oscillation modes. The present study takes a nuanced view of the overall dynamics and their mutual effect on the power output, unlike most existing studies where enhancing the amplitude and frequency of oscillations for an optimal output was the main concern. Factors such as flapper curvature, its asymmetry, and periodicity have been especially highlighted in the context of the output and the corresponding parametric spaces investigated. Interestingly, the increase in piezo-flapper length has seen a reduction in output, though it was instrumental in bringing symmetry back. The study offers comprehensive insights into ideal harvesting regimes and the underlying dynamical mechanisms and can contribute toward the design of future energy harvesting devices.