A packet of short ring-shape perturbations around a crown at the initial stage of merging of a freely falling drop with a still fluid in the impact mode
The paper presents video samples illustrating the rapid evolution of the fine structure of the flow during the merging of a water drop freely falling into a laboratory pool with tap water. At the initial stage of merging in the impact mode, a packet of running periodic annular perturbations was visualized for the first time around the growing crown. The motion of the packet consisting of five to seven rings was tracked by the movement of a group of glares reflected from inclined sections of the liquid surface. The radial distances between the crests of perturbations (analogs of wavelengths) in the packet monotonically increase with distance from the source. The time dependences of the lengths of individual components and the entire packet of annular perturbations, the velocities of its leading and trailing edges, and the frequency of disturbances at selected points were defined. The dependences of the component sizes on the frequency, as well as the cyclic frequency on the wave number of perturbations`, were calculated. Over time, traditional ring capillary waves of greater length, which are formed with some delay, catch up with and absorb the package of primary non-stationary disturbances.
drop impact, experiment, capillary waves, periodic perturbations, dispersion relations
Пакет коротких кольцевых возмущений вокруг венца на начальном этапе слияния свободно падающей капли с
покоящейся жидкостью в импактном режиме
Приводятся выборки из видеофильма, иллюстрирующие быструю эволюцию тонкой структуры течения при слиянии капли воды, свободно падающей в лабораторный бассейн с водопроводной водой. На начальном этапе слияния в импактном режиме вокруг растущего венца впервые визуализирован пакет бегущих периодических кольцевых возмущений. Движение пакета, состоящего из пяти - семи колец, отслеживалось по перемещению группы бликов, отраженных от наклонных участков поверхности жидкости. Радиальные расстояния между гребнями возмущений (аналоги длин волн) в пакете монотонно растут с удалением от источника. Построены зависимости от времени длины отдельных составляющих компонентов и всего пакета кольцевых возмущений, скоростей движения его передней и задней кромок, частоты возмущений в выбранных точках. Рассчитаны зависимости размеров компонентов от частоты, а также циклической частоты от волнового числа возмущений. Со временем традиционные кольцевые капиллярные волны бóльшей длины, которые образуются с некоторым запаздыванием, догоняют и поглощают пакет первичных нестационарных возмущений.
удар капли, эксперимент, капиллярные волны, периодические возмущения, дисперсионные соотношения
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