Droplet impact onto engineered surfaces and related problems

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Droplet impact onto engineered surfaces and related problems

Henman, Nathaniel Isaac John; (2024) Droplet impact onto engineered surfaces and related problems. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Droplet impact is a commonly occurring phenomenon in many industrial and natural scenarios and is the subject of a substantial amount of research. The use of surface engineering to control the dynamics of droplet impact is hugely important in today's world. This thesis tackles various aspects of droplet impact onto two types of engineered surfaces: deformable surfaces and lubricant-infused surfaces. First, the pre-impact phase of droplet impact is analysed by using well established air cushioning models coupled with a general deformable surface model. This system is solved numerically, highlighting a number of key consequences of surface deformability on the pre-impact phase of droplet impact, such as reduction in pressure buildup, increased air entrapment, and considerable delay to touchdown. Connections (including subtle dependence of the size of entrapped air on the droplet velocity, reduced pressure peaks, and droplet gliding) with recent experiments and a large deformation analysis are also presented. The pre-impact behaviour of droplet impact onto lubricant-infused surfaces is also investigated by modifying the surface boundary condition to account for velocity slip. Next, the post-impact phase of droplet impact onto lubricant-infused surfaces is investigated using direct numerical simulation. Using an idealised two-dimensional model of a surface made up of rectangular pillars with a thin layer of lubricant atop, the delicate early stages of impact are analysed, focusing mainly on the extension of the thin splash jet at impact. Results are also compared with solutions for textured, superhydrophobic surfaces, highlighting the key role surface topology plays. Finally, two related problems to the impact scenarios are studied. The first is the horizontal spread of a liquid jet over a lubricant-infused surface. Using a boundary layer approximation, this scenario is modelled for two different length scales, one where the surface can be assumed flat with velocity slip at the interface, and another where the flow in the lubricant and the jet are coupled. Secondly, we study the deformation of a droplet suspended in a uniform flow using a small density ratio approximation. Two temporal regimes are identified and models pertaining to each are presented. The results presented in this thesis will aid in the design of novel non-wetting surfaces for impact scenarios and beyond, as well as highlight possible avenues for further research.

Type:	Thesis (Doctoral)
Qualification:	Ph.D
Title:	Droplet impact onto engineered surfaces and related problems
Open access status:	An open access version is available from UCL Discovery
Language:	English
Additional information:	Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification:	UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering
URI:	https://discovery.ucl.ac.uk/id/eprint/10186657