Wake flow effects on the energy harvesting characteristics of piezoelectric tandem flags

Abstract

In this study, we experimentally investigate the effects of the interaction of piezoelectric flags in the tandem configuration on energy harvesting efficiency. The flags are placed in wake flow behind the bluff body and their flapping behaviors are examined. 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 analyze the effect of wake flow on amplitude, flapping frequency, and harvested power by the piezoelectric flags. Threshold values for energy harvesting of the streamwise gap and freestream velocity are found to be the same for both flags i.e. 1.5 and 0.18m/s, respectively. While analyzing the dynamical behaviors of the flags, inverted drafting phenomenon is observed in flags: the flapping amplitude of the rear flag is increased by excitation from the vortices and wake of the front flag. This kind of interaction helps out in boosting the energy harvesting efficiency based on the random excitations with high amplitude of rear flag. Results show, 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 changes. The highest power is also obtained for the rear flag at streamwise gap equals to 1.75 and freestream velocity of 0.26m/s. The tandem configuration produces 216% more power and remarkably improved the energy harvesting efficiency as compared to the single flag energy harvester.