Fluidic energy harvesting beams in grid turbulence

Much of the recent research involving fluidic energy harvesters based on piezoelectricity has focused on excitation through vortex-induced vibration while turbulence-induced excitation has attracted very little attention, and virtually no previous work exists on excitation due to grid-generated turbulence. The present experiments involve placing several piezoelectric cantilever beams of various dimensions and properties in flows where turbulence is generated by passive, active, or semi-passive grids, the latter having a novel design that significantly improves turbulence generation compared to the passive grid and is much less complex than the active grid. We experimentally show for the first time that the average power harvested by a piezoelectric cantilever beam placed in decaying isotropic, homogeneous turbulence depends on mean velocity, velocity and length scales of turbulence as well as the electromechanical properties of the beam. The output power can be modeled as a power law with respect to the distance of the beam from the grid. Furthermore, we show that the rate of decay of this power law closely follows the rate of decay of the turbulent kinetic energy. We also introduce a forcing function used to model approximately the turbulent eddies moving over the cantilever beam and observe that the feedback from the beam motion onto the flow is virtually negligible for most of the cases considered, indicating an effectively one-way interaction for small-velocity fluctuations.