On impacts, rebounds and icing on air vehicles

The key objectives and aims here are to predict accurately the trajectories and impacts of bodies, droplets and similar objects close to the surface of an air vehicle and to cater for different categories of objects and surrounding fluid flows. Rebounds and ice release may then be confronted. The novel methodology involved is that of mathematical modelling through modern analysis combined with computation. More detail is provided in the following paragraphs.

The project is on fundamental problems of impacts and related phenomena. The focus of the project at first is on the trajectories and impacts of bodies, droplets and similar objects close to the surface of an air vehicle such as a helicopter or airplane. These sometimes messy and complex features are often accompanied by splashes, rebounds from or icing of the surface, or all of the above, which lead on to significant effects in terms of aircraft safety. The splashing is due to the presence of thin water layers (typically 10-100 microns thick) on the wing or fuselage surface. In particular splashes and rebounds tend to affect loss of momentum and heat transfer while ice formation produces sticking and hence further loss. Modelling the above processes is a considerable challenge, with complicated physics and geometries. Most of the modelling to date is based on relatively limited correlations. The project aims to add in significantly more physical reasoning seasoned by mathematical modelling.

Modelling, analysis, computation and experimental connections will be combined with industrial ties (especially at AeroTeX UK who, among other things, design new and improved ice protection systems) in order to address the aforementioned effects for supercooled liquid droplets and ice crystals. We will extend existing work on the impact of one droplet or one body by making it more general. Different categories of objects need to be catered for: small droplets where knowledge is fairly extensive; larger droplets where knowledge is very limited as rebounds and breakups are huge issues; even larger droplets for which there is virtually no previous understanding; ice crystals for which trajectories, sticking and /or bouncing are substantial issues and shape effects play a potentially crucial part. Concerning the latter particles, which tend to be quite thin, the full range of impingement angles is intended to be incorporated in the study and subsequent accretion should be considered in due course. Comparisons between features developing from spherical and non-spherical particles need attending in the sense of their different lift and rotation properties.

Further study can move on to ice release (shedding), improved methodology for the determination (e.g. Lagrangian) of trajectories and its application, a spectrum of particles and how to treat them in groups, and orientation effects in tumbling for example. The present description of the doctoral project is somewhat based on discussions with AeroTeX personnel; the doctoral student may spend occasional secondments at the company at a rate that suits all parties involved.

The project falls under the following EPSRC accepted research areas: complexity science; continuum mechanics; engineering design; fluid dynamics and aerodynamics; mathematical analysis; non-linear systems; particle technology; surface science.