Evolution of vortices at the merging of an ethanol droplet with water in an intrusive mode

The evolution of vortices formed when a freely falling drop of a 95% aqueous solution of ethanol, tinted with brilliant green, merges with water in the intrusive mode has been traced by method of high-speed video recording. The drop smoothly flows into the liquid and forms a subducting lenticular intrusion, in which a weakly expressed ring vortex is formed if the potential surface energy is greater than or of the same order as its kinetic energy. Gradually, the intrusion of lighter liquid begins to float up and contracts around the cavern, which takes on a conical shape. From the center of the pointed bottom of the cavity, which has reached its maximum depth, a compact volume containing a light liquid of droplet is pushed into the thickness of the liquid. After the cavern collapses, the primary intrusion spreads along the free surface of the target fluid. In this case, the submerging volume is transformed into a small spherical vortex, which reaches its maximum depth, and then stops and forms a compact secondary intrusion elongated vertically. Next, the central part of the secondary intrusion begins to flow up and gradually transforms into a new ring vortex. As it approaches the free surface, the diameter of the vortex increases. The slowly rising shell of the intrusion forms the bottle-shaped base of the cylindrical trace of the ring vortex, colored with droplet pigment. Changes in the sizes of the main structural components during the evolution of the flow pattern were traced.