# Impact of liquid droplets with deformable surfaces

Pegg, Michael (2019) Impact of liquid droplets with deformable surfaces. Doctoral thesis, University of East Anglia.

## Abstract

During a droplet impact onto a substrate, splashing is known to be caused by the presence of surrounding gas or by surface roughness. Impact occurring in a vacuum onto a smooth rigid wall results in droplet spreading, rather than development of a corona or prompt splash. In this thesis we present an analytical and numerical study of a third potential splashing mechanism, namely elastic deformation of the substrate. An axisymmetric Wagner-style model of droplet impact is formulated and solved using the method of normal modes, together with asymptotic analysis and numerical methods. We highlight the eﬀect that a ﬂexible substrate brings to the contact line velocity and jet behaviour, demonstrating that oscillation of the substrate can cause blow-up of the splash jet which is absent for a rigid substrate and indicate the onset of splashing.

In chapter 4 we investigate the important role air plays in the pre-impact behaviour of a liquid droplet approaching a solid substrate. A model for the air cushioning of a liquid droplet approaching a partially ﬂexible solid substrate is developed using asymptotic and complex analysis methods. The model is solved numerically using boundary elements and method of normal modes. We show the presence of an elastic plate causes a slowing of the impact and if positioned directly underneath the droplet reduce the overall impact pressure. When the plate is not placed symmetrically touch down is found at only one location, with this touch down point having signiﬁcantly higher impact pressures than initially anticipated.

Finally in chapter 5 we develop a model for the impact of a liquid droplet with an attached air cavity. This preliminary model couples the various parameters inside the gas to the classical Wagner approach for liquid impact and allows us to investigate the evolution of the air cavity and its impact on the motion of the contact points.

Item Type: Thesis (Doctoral) Faculty of Science > School of Mathematics Chris White 14 Apr 2021 10:54 14 Apr 2021 10:54 https://ueaeprints.uea.ac.uk/id/eprint/79745