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Mitchell, Antony James (2019) On the impingement of droplets upon moving films. PhD thesis, University of Nottingham.

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Abstract

Environmental and economic considerations are amongst the key challenges faced in the contemporary aviation industry. Increasing fuel, labour and parts prices, coupled with an ever-tightening legislative environment necessitate a programme of continuing improvement to engine design.

Aero-engines contain bearings housed within bearing chambers and oil is supplied to the bearing for lubrication and cooling purposes, creating a complex two phase environment. Windage and churning in bearing chambers are causes of parasitic losses to the engine, and the high temperatures are a major factor in oil degradation and the formation of carbon deposits. Both of these factors increase the financial and environmental burden to an airline operator. Therefore, it is desired to `tune' the chamber to minimise these behaviours.

A key element of bearing chamber design is the ability to understand and model droplet-film interactions.

A desirable method of modelling is the use Computational Fluid Dynamics (CFD), however these simulations are highly computationally expensive. Therefore, it is desirable to offer empirical correlations for some elements of the droplet-film interaction to reduce the computational costs.

In this thesis research is presented that leads to enhanced understanding and new correlations for droplet impingements on moving films. This represents a significant addition to knowledge as prior the vast majority of available data is for impingements on static films.

The research outcomes were achieved by the use of high speed imaging and Laser Induced Fluorescence (LIF), including Brightness-Based Laser Induced Fluorescence (BB-LIF) applied across a range of droplet impingement conditions. Experimental data was then compared to correlations and understanding from static film studies.

This work focused on parameters to determine the impingement outcome, characteristics of secondary droplets were formed, and the morphology and development of the crown and cavity.

Secondary droplet production showed a good level of comparability to static film research, and four distinct mechanisms of droplet production were categorised.

The crown and cavity dynamics after the impingement were compared to static film models, and modifications proposed to these models in order to better represent moving-film impingements.

In conclusion, it was found that static film knowledge could be applied to moving films, either directly or with modification to account for behaviours unique to moving-film impingements. This is a useful addition to knowledge, and will help guide the development of the next generation of CFD modelling.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Johnson, Kathy Hann, David
Keywords:	fluid mechanics thermodynamics; droplet impingement; laser induced fluorescence; bblif LIF; high speed photography instability aeroengine production crown impingement splashing breakup lamella jetting experimental oblique angled
Subjects:	T Technology > TJ Mechanical engineering and machinery
Faculties/Schools:	UK Campuses > Faculty of Engineering
Item ID:	59391
Depositing User:	Mitchell, Antony
Date Deposited:	14 Feb 2025 09:29
Last Modified:	14 Feb 2025 09:33
URI:	https://eprints.nottingham.ac.uk/id/eprint/59391

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