Full factorial study of the power output of side-by-side piezoelectric harvesters in various types of fractal grid-generated turbulence*

While the majority of the literature in energy harvesting is dedicated to resonant harvesters, non-resonant harvesters have not been studied in as much detail. In this study, the power output of two side-by-side fluidic harvesters from three passive fractal grid configurations (fractal square, fractal ‘I’, and fractal cross patterns) with similar blockage ratios is considered. Fractal grids have been shown to significantly increase the turbulence generated in the flow which is the source of the vibration of the piezoelectric beams. The influence of four parameters has been investigated in a full-factorial experimental study: Beam lengths and configurations, mean flow velocity, distance from the grid and gap between the two beams. Results show that the piezoelectric harvesters in all three fractal grids are capable of producing a larger power output per beam compared to the classical rectangular grid pattern with a smaller blockage ratio (and therefore pressure loss), allowing for a potentially significant increase in the efficiency of the energy conversion process.