Splash: Understanding the Dynamics of High-Speed Drop Impact

Lead Research Organisation: University of Oxford
Department Name: Engineering Science

Abstract

The dynamics of capillary-driven free surface flows, together with turbulent behaviour are, arguably, some of the most challenging topics in fluid dynamics. They involve complex flows evolving across several length and time scales. The dynamic fluid processes involved during drop formation and disintegration are fascinating but extremely complicated, with time-dependent fluid interface disruptions.

A drop impacting on to a surface (which can be a solid, liquid (including a thin film on top of a solid), or granular) can, among other results, splash, bounce back or simply spread. What kind of dynamics will be observed depends not only on the liquid properties and speed of the drop, but on other parameters, such as the atmospheric pressure, the surface's roughness, stiffness and temperature and other substrate properties. While in some industrial applications splashing is desired (e.g. cooling and combustion), it is to be avoided at all cost in others (e.g. inkjet printing or in the prevention of the spreading of infectious diseases).

Current advanced mathematical techniques combined with state-of-the-art computational power, and technological advances in experimental imaging techniques, mean that we are in a unique position to finally observe and model in unprecedented detail and at unprecedented speeds how a drop forms and evolves, or how it disintegrates after a high-speed impact.

Splashing is one of the most fascinating, albeit challenging, topics in the field of drops, due to its complexity and beauty. However, the exact mechanisms triggering a splash have remained elusive. With the help of cutting-edge ultrahigh speed photography, modern ultrahigh resolution numerical simulations and asymptotic theory the main objective of the proposed research is to reveal the dynamics underlying and triggering a splash. In particular, we will aim at:

1- Identify the role that the pressure build-up in the vicinity of the impact zone has over the speed of the liquid jet that eventually breaks up forming the splash.
2- Understand the contributions due to pure viscous and viscoelastic effects of both the drop and target. Recent experimental investigations indicate that the transition from prompt splash to corona splash can be triggered by increasing the viscoelasticy of the working fluid. However, the exact influence of such property is currently unknown.
3- Obtain velocity maps of the surrounding gas during the drop impact and consequent splash in order to further validate our numerical simulations.
4- Explore the influence that fluid properties such as viscosity, viscoelasticity have on the final dynamics of the splash.
5- Based on the above, explore techniques to suppress splashing.

The first part of this this research will involve carrying out a series of systematic experiments, simulations, and theory, of the impact of drops onto (immiscible) substrates of varying viscosity. The use of liquids such as silicone oils, for example, would allow the variation of viscosity from 0.1 to 1,000,000 mPa s while keeping both density and surface tension constant. Ultrahigh speed fluorescence imaging will allow us to study the complex contact line behaviour. These experimental results coupled with Volume of Fluid simulations and theoretical arguments will provide a full history of the dynamics. It is planned that the influence of the surrounding gas will also be explored by performing experiments in a reduced pressure environment.

These objectives are major undertakings, and a close collaboration with Prof. S Thorodssen at KAUST, Prof. J Oliver and Dr. R. Cimpeanu at Oxford (Mathematical Institute), and Prof. A. Antkowiak and colleagues at UPMC/Sorbonne will be invaluable in providing access to unique instrumentation and equipment, to theoretical asymptotic theories used in impact problems, and to the latest fluid flow simulation tools and necessary computing power, respectively.

Publications

10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509711/1 01/10/2016 30/09/2021
2118171 Studentship EP/N509711/1 01/10/2018 31/03/2022 Benjamin David Fudge