Energy harvesting prospects in turbulent boundary layers by using piezoelectric transduction

Thin flexible cantilever beams with patches of piezoelectric materials or surrogate beams with attached strain gages have been electromechanically characterized for energy harvesting inside turbulent boundary layers. A turbulent boundary layer carries mechanical energy distributed over a range of temporal and spatial scales and their interaction with the immersed piezoelectric beams results in a strain field which generates the electrical charge. This energy harvesting method can be used for developing self-powered electronic devices such as flow sensors. In the present experimental work, various energy harvesters were placed in the boundary layers of a large scale wind tunnel with Reθ between 2000 and 7500. The orientation of the beam relatively to the incoming flow and the wall was found to be critical parameters affecting the energy output. “Power maps” are presented for various roll and pitch angles as well as external flow velocities. The role of large instantaneous turbulent boundary layer structures in this rather complex fluid-structure interaction is discussed in interpreting the electrical output results. The forces acting on the vibrating beams have been measured dynamically and a theory has been developed which incorporates the effects of mean local velocity, turbulence intensity, the relative size of the beam׳s length to the integral length scale of turbulence, the structural properties of the beam and the electrical properties of the active piezoelectric layer to provide reasonable estimates of the mean electrical power output.