Multiple Emissions of Splashes upon Drop Impact
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Multiple Emissions of Splashes upon Drop Impact Yu. D. Chashechkina,* and A. Yu. Ilinykha,** Presented by Academician D.M. Klimov August 13, 2020 Received August 14, 2020; revised August 14, 2020; accepted August 16, 2020
Abstract—For the first time, photo and video detection is carried out for all groups of small droplets (splashes) emitted when a drop of 0.2 < D < 0.5 cm in diameter falls with a velocity of 1 < U < 4.05 m/s into a pool with water. In the splash-formation mode, groups of droplets are ejected in echelons first from the tops of spikes on the veil around the primary contact area, then, from the spikes on the edges of the split shells of the crown, and, finally, from the teeth of its chevron. The first splashes fly out radially, and the next move inward around the cavity and vertically upward. The splash sizes grow with time from 0.1 to 1.0 mm. Their velocities decrease from 20 to 1 m/s, and the intervals between groups increase from 50 μs to 2.5 ms until the beginning of smoothing of the crown teeth (t ≈ 17 ms). The acceleration of the droplets is facilitated by the conversion of the available potential energy when the free surfaces of the merging droplets are annihilated. Keywords: drop, spray, veil, spikes, splash, thin jets (trickles) DOI: 10.1134/S1028335820100067
The splashes escaping into the air when drops fall into a liquid play an important role in nature and technology. The “condensation centers,” the remnants of sea droplets carried out by air jets into the upper atmosphere, affect the formation of clouds, the local weather, and the climate [1]. Viruses and bacteria enter the atmosphere along with the spray [2]. Raindrops and large blobs of water, which are formed during their merging, moisten the soil, the particles of which are captured by escaping splashes, which carry out soil pathogens into the air [3]. The dropping systems are used for cooling various devices from microcircuits in terrestrial conditions [4] to power plants in space [5], the durability of which depends on the number of splashes causing the loss of the refrigerant. In the investigations, which began in the 19th century with the development of spark illuminators [6], in addition to splashes, a veil was noticed, i.e., a flat trickle escaping from the region of coalescence of liquids, which is opposite to the annular trickle on the crown [7], and droplets flying inward [8]. The droplet substance is distributed over the surface of the liquid in fibers [9], the formation of which is affected by the rapid conversion of the available potential surface energy during the coalescence of liquids [10]. It is of practical interest for determining the geometry of the a Ishlinsky Institute for Problems in Mechanics of the Russian Academy of Sciences, Moscow, 117526 Russia *e-mail: [email protected] **e-mail: [email protected]
spray field and the duration of the process of their emission. In this study, we for the first time traced the change in the sources of splashes, when a falling drop merges with a liquid in the mode of spla
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