Experimental Investigation of Two Conventional Energy Harvesting Eels in Tandem Configuration

Abstract

The interaction of two tandem conventional piezoelectric flag configuration in a uniform flow was investigated. The piezoelectric flags convert the kinetic energy of flowing water into electrical energy based on vortex-induced vibration. The piezoelectric flags were placed in the wake of a bluff body and their flapping behavior is investigated in terms of the flow velocity and streamwise gap between flags. The flags showed two types of flapping modes; flapping mode and biased mode. Inverted drafting was observed in flags: the drag force on one flag is increased by excitation from the wake of others. The output voltage of flags increased by increasing the flow velocity because the forces applied on the piezoelectric flag increases by increasing the flow velocity. The flapping amplitude and output voltage of the downstream flag is found to be larger than the upstream flag. The experiments were performed by placing two conventional piezoelectric flags in tandem configuration in the wake of bluff body in low-speed water tunnel by varying the flow velocity (V) and streamwise gap (Gx) behind an inverted C shaped cylinder to find the effect of vortices produced from the bluff body on flapping amplitude, flapping frequency and the voltage generated by the piezoelectric flags. Image processing technique was used to find out peak to peak amplitude and Fast Fourier Transform (FFT) was used to find out a dominant flapping frequency in MATLAB. The output voltage from the piezoelectric flag was measured by using DAQ (a module in Lab View for receiving analog output voltage