Walton, Karl (2015) Rolls-Royce Trent series compressor blade surface topography its development and influence on aerodynamic performance. Doctoral thesis, University of Huddersfield.

The rapidly expanding civil aerospace sector is subjected to ever increasing pressure to be both sustainable and competitive. The research reported in the current thesis forms a part of the significant R&D effort of Rolls-Royce in response to this pressure.
A broad based approach is taken to evaluating compressor blade surface finish with the objective of improving manufacturing and operating efficiency. Technical developments made as part of the current work is also intended to support future research in this important field. Compressor blade surface finish is emulated in the lab to detail its topographical development through the critical final polishing stage of processing. Based on existing surface standards a new characteristic developmental pattern and nomenclature is described for this finishing process. In addition, ‘edge shadowing’ a novel surface texture distribution is reported showing mass finishing to be non-uniform over a flat surface.
The surface texture of exemplar ’as manufactured’ compressor blades is assessed and a protocol for areal parametric characterisation is developed. The protocol includes consideration of; surface texture homogeneity, local & global sample weighting, sampling efficiency, and key characteristic areal parameters, with their specification levels and confidence intervals.
This detailed examination of mass finishing and the surface texture it produces will help improve process control and optimise economy.
To improve the ongoing assessment of compressor performance degradation in service, a series of recovered compressor blades are characterised. Predominantly automated techniques are developed to assess compressor blade side and leading edge character. Key trends in surface topography on individual blade surface regions are reported along with broader degradation trends throughout the compressor. Leading edges are shown to be characteristically prone to greater degradation and levels of surface roughness, though elevated leading edge roughness is better correlated with deposits than with erosion. Proper analysis of aerodynamic losses due to aerofoil surface roughness requires the use of techniques with conflicting requirements. Thus in the current context the replication of metallic test aerofoils in thermally insulating resin is required. A method for this replication and its validation are presented.
To investigate the underlying mechanisms of drag loss due to surface roughness a series of rough test aerofoil surfaces were parametrically characterised and wind tunnel tested. The well-established but incomplete correlation between drag loss and mean surface roughness amplitude (Sa) is then refined with other selected parameters that more fully represent surface topography.

Final thesis - WALTON.pdf - Accepted Version
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