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Дата последнего поиска статьи во внешних источниках: 2 февраля 2018 г.
Аннотация:The collision of water drops against small targets was studied experimentally by means of a
high-speed photography technique. The drop impact velocity was about 3.5 m/s. Drop diameters
were in the range of 2.8–4.0 mm. The target was a stainless steel disk of 3.9 mm diameter. The drop
spread beyond the target like a central cap surrounded by a thin, slightly conical lamella bounded
by a thicker rim. By mounting a small obstacle near the target, surface-tension driven Mach waves
in the flowing lamella were generated, which are formally equivalent to the familiar compressibility
driven Mach waves in gas dynamics. From the measurement of the Mach angle, the values of some
flow parameters could be obtained as functions of time, which provided insight into the flow
structure. The liquid flowed from the central cap to the liquid rim through the thin lamella at
constant momentum flux. At a certain stage of the process, most of the liquid accumulated in the rim
and the internal part of the lamella became metastable. In this situation, a rupture wave propagating
through the metastable internal part of the lamella caused the rim to retract while forming outwardly
directed secondary jets. The jets disintegrated into secondary droplets due to the Savart–Plateau–
Rayleigh instability. Prior to the end of the retraction, an internal circular wave of rupture was
formed. It originated at the target and then it propagated to meet the retracting rim. Their meeting
resulted in a crown of tiny droplets. A theoretical analysis of the ejection process is
proposed.