Experimental investigation into the streamwise circulation generated by bio-inspired pitching panels

Stereoscopic particle image velocimetry and performance measurements are used to inves-tigate the performance characteristics and unsteady, three-dimensional wakes of bio-inspired pitching panels with varying trailing edge geometries. The planform shapes of the five panels were selected as rudimentary approximations of the shapes of caudal fins found in nature. All panels were sinusoidally pitched about their leading edges through five different pitching am-plitudes within a constant free stream flow, generating five unique Strouhal numbers for each specific panel geometry. It was found that increases in Strouhal number for a specific panel geometry, achieved through increases in pitching amplitude, correspond to the generation of larger maximum values of the instantaneous streamwise circulation, as well as larger values of the mean streamwise circulation. It was shown that, when actuated at similar Strouhal num-bers, panels with different trailing edge shapes are able to produce different behaviors in terms of streamwise circulation. With respect to commonly used performance metrics, the pointed panels tend to outperform the forked panels, despite the additional increase in streamwise circulation and the utilization of a lower aspect ratio propulsor planform.