Evolution of the heavy impacting droplet: Via a vortex ring to a bifurcation flower

We herein report an instability of a vortex ring, produced from the impact of a droplet of glycerol solution, penetrating in a water pool. The morphological and motional evolutions of the vortex ring have been captured using the high-speed shadowgraph technique. It is identified that the vortex ring undergoes a two-stage evolution with the disintegration as the turning point, namely, damping penetration and cyclic bifurcation, during which the viscous drag and gravity alternatingly dominate the penetrating behavior. We further propose two unified descriptions, respectively, for the penetration of the vortex ring before and after the disintegration and establish the instability criterion for both the disintegration and the bifurcation as well.