The Laws of the Matter Distribution in a Colored Free-Falling Drop in a Transparent Target Fluid (Review)

The results of the visualization of the matter transfer processes in colored free-fall drops, which mix with a transparent target fluid are analyzed. The parametrization is carried out basing on the system of fundamental equations of fluid mechanics which includes the equations of state for the density and the Gibbs potential. The contribution of different mechanisms of energy transfer is discussed; these are the macroscopic (including flows, waves, and vortices) and microscopic (dissipative and conversional) ones. The radiation transfer effect is not considered. The technique of the present-day experiments is descried, which allows to record accompanying acoustic signals together with the highly-resolving videorecording of colored flow pictures. The flow structure, dynamics, and energetics are analyzed for different density ratios of the confluent fluids and the kinetic and potential surface energies (PSE) of the drop. The conditions of the establishment of certain selected regimes, such as intrusive drop inflow, impact breakdown in fibers, and an intermediate hovering and rebound regime, are determined. A drop flowing smoothly into the fluid thickness at a small contact velocity in the intrusive regime forms a connected body. Thin trickles containing the matter of both media are formed in the contact spot in the impact mode. The fibrous wakes of the trickles form lineate and reticular structures on the fluid surface and within its thickness. In the intermediate regime the drop can hover on the fluid surface, touch it, merge partially with it, and rebound with the loss of the matter. The evolution of gas cavities and bubbles radiating acoustic packets is traced. The necessity of taking account for all the mechanisms of total energy transfer in describing hydrodynamics and acoustics of drop flows is noted.