Design and Analysis of a Vortex-induced Bi-directional Piezoelectric Energy Harvester

Abstract Vortex-induced vibrations (VIVs) in wind flows have been considered as a promising energy source for piezoelectric energy harvesting. However, a conventional VIV-based piezoelectric energy harvester can only scavenge wind energy from one direction. In this study, we propose a vortex-induced bi-directional piezoelectric energy harvester that can collect wind energy in two orthogonal directions, namely the horizontal and vertical directions. The proposed bi-directional harvester is composed of a U-shaped beam, a pair of piezoelectric patches, and a foam cylinder attached to the center of the beam. The theoretical model of the proposed harvester is established based on Euler-Bernoulli beam theory. Rayleigh oscillators are adopted to model the wake oscillation of the harvester. The proposed harvester is firstly examined under base excitations of two orthogonal directions to validate its resonant frequencies. Subsequently, the dynamic responses of the proposed harvester in vortex-induced vibrations is simulated and the corresponding experiments are carried out. The proposed harvester demonstrates the capability of harvesting wind energy from two directions of wind flow. Parametric analysis is conducted to evaluate the influence of the lengths of the side beam and main beam on the performance of the proposed harvester. The results demonstrate that shortening the side beam significantly increases the lock-in wind speed of the horizontal mode but has little impact to that of the vertical mode. On the other hand, changing the length of the main beam affects the vertical mode more than the horizontal mode. Overall, this study demonstrates that the proposed harvester can scavenge wind energy from two directions of wind flow. The geometry of the U-shaped structure can be adjusted to adapt the harvester to the wind speed in the environment.