Hydrodynamic energy harvesting analysis of two piezoelectric tandem flags under influence of upstream body’s wakes

Abstract

In this study, the effects of the interaction of piezoelectric flags in the tandem configuration on energy harvesting in a wake flow are experimentally investigated. The flags are placed behind the bluff body and their flapping behavior is examined in terms of the flapping frequency and amplitude (peak to peak motion). The experiments are performed in a low-speed water tunnel by varying the flow velocity and streamwise gap behind an inverted C-shape cylinder to determine the influence of wake flow on the oscillating amplitude, flapping frequency, and harvested power by the piezoelectric flags. Threshold values for energy harvesting of streamwise gap and water speed are found to be the same for both flags, 1.5 and 0.18 m/s, respectively. The results show that inverted drafting is observed in flags in which the flapping amplitude of the rear flag is increased by excitation from the vortices and wake of the front flag. This interaction boosts the energy harvester efficiency based on the flapping frequency and the random excitations with high amplitudes. It is observed that as the streamwise gap in-between the flags changes, the influence of the front flag on downstream flag alters, and dynamical behavior of front flag show variation when the distance between bluff body and front flag varies. The highest power is also obtained for the rear flag at a gap of 1.75 and water speed of 0.26 m/s. The tandem configuration produces 116% more power and significantly improves the energy harvesting efficiency as compared to the single flag energy harvester.