Experimental Investigation of the Evolution and Head-On Collision of Elliptic Vortex Rings

The head-on collision process of elliptic vortex rings was experimentally investigated using flow-visualization technique as well as particle image velocimetry (PIV). Elliptic vortex rings were generated by the movement of a free moving elliptic piston-cylinder arrangement. It was found that the Q value is positive in the vortex core region while negative in the regions around the vortex core, which indicates the rotational effect is dominated in the vortex core and strain effect is dominated around the vortex core. When two elliptic vortex rings move toward each other, both rings slow down and expand in diameter direction until they merge and expand in diameter direction rapidly. The collision process of two elliptic vortex rings and the newly generated vortex structure after collision are dominated by the elliptic vortex ring with larger aspect ratio and the trajectories of vortex core almost coincide in different Reynolds numbers.