Oleg Goushcha

Interactions of vortices with a flexible beam with applications in fluidic energy harvesting

A cantilever piezoelectric beam immersed in a flow and subjected to naturally occurring vortices such as those formed in the wake of bluff bodies can be used to generate electrical energy harvested in fluid flows. In this paper, we present the pressure distribution and deflection of a piezoelectric beam subjected to controlled vortices. A custom designed experimental facility is set up to study the interaction of individual and multiple vortices with the beam. Vortex tori are generated by an audio speaker and travel at controlled rates over the beam. Particle image velocimetry is used to measure the 2-D flow field induced by each vortex and estimate the effect of pressure force on the beam deflection.

The Effects of Turbulence Length Scale on the Performance of Piezoelectric Harvesters

Turbulent flows carry mechanical energy distributed over a range of temporal and spatial scales and their interaction with a thin immersed piezoelectric beam results in a strain field which generates 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 a turbulent boundary layer or inside a decaying flow field of homogeneous and isotropic turbulence. The role of large instantaneous turbulent 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. Experiments have been carried out in which these fluidic harvesters are immersed first in inhomogeneous turbulence like that encountered in boundary layers developing over solid walls and homogeneous and isotopic turbulence for which a simplified analytical description exists. It was found that there is a non-linear effect of turbulence length scales on the power output of the fluidic harvesters.Copyright

Fluidic harvester under train of frozen boxcars (TFB) loading: a parametric study

The Train of Frozen Boxcars (TFB) model has been developed for a continuous piezoelectric cantilever fluidic harvester to simplify the effective one-way interaction between the fluid and the structure for certain flows. The TFB model treats the force due to vortex or turbulent flow as a series of boxcars of different amplitudes, widths and separations advected with a constant velocity over a piezoelectric beam. In this paper, the effect of five parameters, namely the number, amplitude, width, spatial separation and advection speed of the boxcars in the TFB forcing model, is studied for four different forcing scenarios. It has been observed that an increase in the amplitude or advection velocity of the boxcars leads to an increase in the power output, whereas a saturation limit in the power output is observed with an increase in the width or number of boxcars. More importantly, however, it is concluded that the separation between boxcars is the determining factor in maximizing or minimizing the power output from the harvester.