Unraveling the interplay of two counter-rotating helical vortices

Our experiments examine the interaction between two coaxially aligned helical vortex systems induced by two counter-rotating propellers of slightly different diameters operating in a water tunnel. Visualizations show that the two helix structures merge and breakup in the regions of closest distance and strongest vorticity. A reconnection process follows, resulting in the formation of isolated vortex rings advected by the accelerated flow of the propeller system.