Regimes of impact close to a surface’s edge: change in sheet fragmentation regimes

Regimes of impact close to a surface’s edge: change in sheet fragmentation regimes

Sheet fragmentation from impact of a drop near a surface edge as mimic of impacts on leaves involving drop-on-drop Crescent-moon fragmentation. The edge fragmentation causes the sheet’s right part to expand in the air, with fragmentation characterized by an unsteady rim bordering the sheet in the air also governed by the unsteady local Bond = 1 and edge ejections of drops on the sides, contact line retraction, and final collapse of the sheet that can lead to violent ligament breakup.

Image: Time evolution of the sheet in the air for d/R0 =4.4,3.2,2,and1.3 (top to bottom) and We=1340. Rows 1, 2, 3, and 4 correspond to the retraction scenarios I, II, II, and III, respectively. Snapshots in the same column are taken at the same time t post impact, with t = 0, 3, 6, 8, 11, 12, and 14 ms from left to right. Column (a) illustrates the position of the drops right before impact, with respect to the edge. The scale bar is 5 mm.

Context: Asymmetric liquid sheet fragmentation is ubiquitous in nature and potentially shapes critical phenomena such as rain-induced propagation of foliar diseases. We investigate the formation and fragmentation of a liquid sheet upon impact of a drop close to the edge of a solid substrate. Both the impact Weber number and the offset, the distance from the impact point to the edge, are systematically varied. Their influence on the kinematics of the liquid sheet and the subsequent statistics of droplet ejection are rationalized. Three major asymmetry scenarios are identified and linked to distinct droplet ejection patterns. Scaling laws are proposed to rationalize these scenarios based on impact parameters. Selection of droplet emission from various mechanisms are highlighted and the implications on propagation of contaminated fluids from impact discussed.

Source: Lejeune, S., Gilet, T., and Bourouiba, L. (2018) Edge-effect: Liquid sheet and droplets formed by drop impact close to an edge. Physical Review Fluids. 3, 083601. PDF. 

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