On the competition between leading-edge and tip-vortex growth for a pitching plate

The interaction between leading-edge-vortex and tip-vortex development on a low-aspect-ratio plate has been investigated and compared to a nominally two-dimensional rectangular flat plate. Simultaneous to force measurements, three-dimensional particle tracking velocimetry (3D-PTV) was used to characterize the instantaneous flow field on the suction side. An integration of the spanwise circulation distribution for the two-dimensional case indicates that the leading-edge-vortex formation process is correlated with the convective time and not with the instantaneous pitch angle. However, for the finite plate, it is found that the tip-vortex formation process is correlated with the instantaneous pitch angle instead. Since leading-edge vorticity is convected inboard by tip-vortex-induced spanwise velocity, leading-edge-vortex growth is found to be retarded in the tip region. Finally, with the aid of Lagrangian particle tracks, the leading-edge and tip vortices are found to grow distinct from one another, that is, no leading-edge vorticity is drawn into the tip vortex. However, the tip vortex is found to influence the leading-edge-vortex dynamics through inboard transport of leading-edge vorticity and is therefore responsible for vortex compression at the mid-span.