Analysis and simulation of instabilities in axial compressors: engine model integration.

The field of jet engines has reached such a level of advancement and technological refinement that contributing to the current state of the art is getting more and more difficult over the years. Despite this engineering saturation, engine reliability remains under strict scrutiny by every manufacturer. One of the main challenges in keeping such a complex system safe is developing real-time simulation algorithms that are able to predict all possible malfunctions, either to avoid them or to stop them in time. The main goal of this thesis is to present a complete simulation of a turbojet engine (namely a GE-J85) which is able to identify anomalies in the compressor, like rotating stall or surge. The simulation introduces the Moore-Greitzer model to the code previously developed by eng. Valerio Timo in his MSc thesis, and aims at recognising the parameters that should reveal the occurrence of one or both of the instabilities. The actual compressor map was replaced with a new, approximated one, obtained by nondimensionalising the pressure ratio/ mass flow rate plane first, and then by interpolating the experimental values with a third order polynomial. This allowed switching from a discrete distribution of points to an analytical function, so that even the part of the map which is behind the surge line, and that gets usually neglected, could be represented. The Moore and Greitzer's differential equations were then introduced in the engine model, with the aim to perform a transient simulation that could - under specific circumstances - foresee the presence of instabilities. A wide range of values for both the engine end the mathematical model was employed in the analysis to test the accuracy and reliability of the simulation. Finally, the results were discussed and eventual improvements to the system were commented on.