Abstract:
The objective of the work described in this thesis is twofold; to elucidate the nature of
stall and
surge in an axial flow aeroengine compressor, and to improve on current
computational stall modelling techniques. Particular attention is paid to
the initial stages of the stall/surge transient, and to the possibility of using active control
techniques to prevent or delay the onset of stall/surge.
A detailed
analysis is presented of measurements of the stalling behaviour of a Rolls-
Royce VIPER jet engine, showing a wide variety of stall inception and post-stall
behaviour. Stall transients are traced from disturbances through to stable
rotating stall or axisymmetic surge. The stall inception pattern at nearly all speeds is
shown to conform to the short circumferential length scale pattern described by Day
[1993a].
A multiple compressors in parallel stall model is developed using conventional stall
modelling techniques, but extended to include the
effects of the jet engine environment
The model is shown to
give a good representation of the overall stalling behaviour of
the
engine, although the details of the stall inception period are not accurately
predicted. A system identification technique is applied to the results of the model in
order to
develop a method of active control of stall/surge.
A new stall model is introduced and
developed, based on a time-accurate three
dimensional (but pitchwise averaged) solution of the viscous flow equations, with
bladerow performance represented by body forces. The flow in the annulus boundary
layers is calculated directly, and hence this new method is sufficiently complex to
model the initial localised disturbances that lead to
stall/surge. At the same time the
computational power required is compatible with application to long multistage
compressors.
