Simultaneous impact of droplet pairs on solid surfaces
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Published version
Author(s)
Goswami, Anjan
Hardalupas, Ioannis
Type
Journal Article
Abstract
This study investigates the dynamics of the simultaneous impact of two droplets on a dry substrate. We develop a new micro-controlled droplet generator that releases two equally sized water droplets simultaneously on-demand, with no trailing droplets. The impact Weber number, based on impact droplet size and velocity, and the inter-droplet spacing relative to the impact droplet size are varied in the ranges of 54 to 155 and 1.32 to 2.25, respectively, leading to the strong interaction of the spreading lamellae that form a central uprising sheet, which eventually deposits or breaks into tiny droplets. We analyse the impact processes for both deposition and splashing of the uprising sheets. Simultaneous high-speed imaging from two orthogonal views of the droplet impacts quantifies the three-dimensional structure of the sheet morphology, including the temporal evolution of the rim-bounded ‘semilunar’ shape, surface waves, rim corrugations and finger formation, and deposition or splashing of the liquid sheet. The characteristics of the sheet surface waves and the rim instabilities are quantified. Novel scaling is developed for the maximum sheet height, sheet width and thickness, which considers the geometrical constraints and mass balance of the interacting lamellae to describe the temporal evolution of a ‘semilunar’ uprising sheet and is in good agreement with the measurements. The uprising sheet splashing generates larger droplets than those from splashing of single-droplet impacts, and it occurs due to the end-pinching of sheet fingers and at conditions that single-droplet impacts lead only to liquid deposition.
Date Issued
2023-04-25
Date Acceptance
2023-03-16
Citation
Journal of Fluid Mechanics, 2023, 961, pp.1-37
ISSN
0022-1120
Publisher
Cambridge University Press
Start Page
1
End Page
37
Journal / Book Title
Journal of Fluid Mechanics
Volume
961
Copyright Statement
© The Author(s), 2023. Published by Cambridge University Press. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
License URL
Identifier
https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/simultaneous-impact-of-droplet-pairs-on-solid-surfaces/D1C4CAF145338294CF265597970912FD
Publication Status
Published
Article Number
A17
Date Publish Online
2023-04-25