Comparative experimental investigation and effectiveness of sphere- and cylinder-based piezoelectric energy harvesters

Abstract

This letter presents an idea of employing sphere as a bluff body subjected to cross flows for improving piezoelectric energy harvesting from flow-induced vibrations (FIVs). Unlike cylindrical bluff bodies used in most of previous studies, the proposed harvester with sphere configuration can be freely settled in horizontal and vertical directions without reconfiguration. Experimental results show that the aspect ratio (length of beam to diameter of sphere) and mass ratio between sphere and beam have great effects on output performance of the energy harvester. It is found that the optimal aspect ratio and mass ratio are 1.7 and 0.15 where the harvester has a broadband lock-in between 2 m s−1 and 6 m s−1 and a maximum output average power of 190 μW. This is attributed to variations of the natural frequency and aerodynamic force varying with the sphere diameter, resulting in multiple modes responses to significantly enhance the output power. Furthermore, the output comparison between sphere- and cylinder-based energy harvesters indicates that sphere is superior in the case of horizontal placement, while for the vertical placement as the wind speed is below 4 m s−1 it is better to use sphere, but beyond 4 m s−1, cylinder is superior within the considered wind speed region. The present study gives a new design for effectively harvesting energy from FIVs according to available wind speed.