Transfer of Matter at the Initial Stage of Cavity Formation in the Impact Mode of Merging a Freely Falling Drop

Using the methods of scientific photography and videography, the flow pattern and distribution of matter of a free-falling fluid drop in a resting target fluid at the initial stage of cavity formation are recorded. The experiments are performed in the range of parameters of the impact mode of coalescence when the kinetic energy of the drop exceeds its available potential surface energy (APSE). To register the color image, the flow pattern is simultaneously illuminated by several light sources including matrix LEDs and fiberoptic sources of a constant light. The planning and interpretation of the experimental results are carried out considering the properties of complete solutions of the fluid mechanics’ fundamental equations’ system, as well as mechanisms of the energy transfer and conversion. The experiments are performed with a single drop of potassium permanganate solution falling into water. In the impact mode, the drop begins to lose its continuity at the initial contact when a veil and thin trickles are formed, whose velocity exceeds the drop contact velocity. From the tops of the trickles, small droplets are thrown into the air, whose size grows with time. On the surface of the fluid, the trickles leave dyed traces that form line and mesh structures. Some of the trickles penetrate the cavity bottom and form an intermediate layer. In it, the trickles are separated by layers of the target fluid. The molecular diffusion processes equalize the density difference and form an intermediate layer, which is outlined by sharp boundaries, under the cavity.