Design Parameters Affecting the Performance of Vortex-Induced Vibration Harvesters.

Vortex-induced vibration harvesters are usually equipped with small piezoelectric patches mounted near the cantilever clamp, where the largest longitudinal stress occurs. This paper, aiming to improve energy harvesting performance, investigates the possibilities of extending the patch length and modifying the length and mass of a bluff body mounted on a harvester to induce vortex shedding. A novel analytical model based on dimensionless numbers is presented to determine the output voltage generated by a cantilever harvester subjected to periodic vortex shedding. This model highlights the design parameters having the largest influence on harvester performance and provides guidance to the planning of experimental tests and the interpretation of experimental results. Some prototype harvesters with different designs are built. First, experimental tests are carried out to identify the natural frequencies and damping ratios of the prototypes; then, the prototypes are tested in a wind tunnel to assess energy harvesting performance. The best performance is achieved when the patch length is about 20% of the cantilever length, the bluff body is long, and its mass reaches the minimum value. This result agrees with the prediction of the model.