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Experimental studies on head-on collision of two vortex rings were carried out in air using the flow visualization method of NH 4 Cl smoke. As the rings approached each other, their diameters increased due to the mutual interaction. Measurements of the trajectories and velocities of the rings were compared with the numerical simulation and they showed good agreement. The trajectories of the colliding rings were different from the trajectories of one ring moving against a solid wall. The difference seems to be due to the boundary layer on the wall. At higher initial speed, the two vortex rings split into a number of small vortex rings after the cross-linking of vortex filaments.
Yuko Oshima (Sun,) studied this question.