Abstract:
Gas turbine sub-idle performance modelling is still in an early development stage and
this research aims to provide and improve present techniques, for modelling of
windmilling and transient windmilling relights, through to groundstart simulations.
Engine ATF data was studied and used to align models created within this research for
low and high bypass engines, and compare these models simulation results.
Methods for the extrapolation of component characteristics are improved and performed
in linearised parameter form, and the most efficient approach discussed.
The mixer behaviour is analysed and recommendations of off-design mixer behaviour
representation in a sub-idle model are proposed and performed within the modelling.
Combustion at sub-idle conditions is investigated with regards to the loading parameter
definition, and also its representation for the influence of evaporation rate being limiting
to overall combustion efficiency. A method is proposed on extrapolating and
representation of the combustion characteristic.
Compressor behaviour and the blade torques at locked rotor and windmilling conditions
are studied using 3D CFD, producing insight and discussion on CFD suitability and
what it can offer at these operating conditions. From the CFD studies generic loss
coefficients were created for all compressor blades, from which a zero speed is created
for the whole compressor, from a theoretical stage stacking calculation. This zero-speed
curve is shown to allow interpolation of component characteristics to the sub-idle
region, improving the definition and a predictive approach. A windmilling conditions
cascade test rig is proposed, designed and built for validating the CFD loss coefficients.
The findings and discussions within this thesis provide useful reference material on this
complicated and little documented area of research. The modelling and methods
proposed, provide great advancement of the research area, along with further integration
of the Cranfield UTC in performance with Rolls-Royce.
