Propulsion and Turbomachinery

Module aims

This module covers the fundamental theory of jet engines, including ramjets, turbojets and turbofans. The module starts with overall thermodynamic cycle analysis of typical aeroengine designs before proceeding to detailed aero-thermal analysis of individual components including subsonic and supersonic intakes, compressors, combustors, turbines, afterburners, and convergent-divergent nozzles, leading to comprehensive full-engine performance calculations. 

Learning outcomes

On successfully completing this module, you should be able to:
1. Demonstrate understanding of the basic concepts of aircraft propulsion and the parameters characterising engine performance.
2. Apply thermodynamic cycle analysis to evaluate the performance of gas turbine engines.
3. Integrate performance characteristics of individual gas turbine engine components into calculations of overall performance of ramjet, turbojet and turbofan engines.
4. Justify choice of fundamental intake, combustor and nozzle designs for a given engine cycle. 
5. Demonstrate understanding of the basic concepts of the aerodynamic theory of cascades and apply this to predict the performance of ideal cascades for given cascade geometry and cascade RPM.
6. Explain the principles of the compressor and turbine matching in a turbojet engine.  

Module syllabus

General engine layout: intake, compressor, fan, combustion chamber, turbine, nozzle. Twin spool and fan engines. Bypass ratio. Reheat: description of components.
Engine performance: thrust equation, thermal efficiency, propulsion efficiency, overall efficiency, specific thrust, specific fuel consumption.
Gas turbine (Brayton) cycle, and its use for analysis of engines  Effects of component losses: compressor and turbine losses, adiabatic efficiencies, combustion chamber losses, mechanical losses. Calculating the engine performance characteristics for a given flight regime and performance characteristics of the components. Cycle analysis for turbojet engines: optimal compressor pressure ratio. Reheat: analysis of effect on engine performance.
Subsonic and supersonic intakes: normal shocks and oblique shock waves, supersonic intake idea, Intake failure due to Mach reflection in the intake, supersonic intake failure due to boundary layer separation. 
Supersonic converging-diverging nozzle, quasi-one-dimensional flows, choked nozzle, maximum thrust, subsonic intake, additive drag.
Combustion: principles of design of turbojet engine combustors, combustor types, combustor requirements, zonal combustion, primary combustion zone, fuel injection, stability loop, pressure losses and combustion intensity.
Turbomachines: types of machines, compressors and turbines, stators and rotors, description of mechanical arrangements. Aerodynamics of axial flow machines: basic cascade theory, ideal cascade calculation, blockage, deviation, losses, friction losses, secondary losses, stall losses, shock losses, repeating stage and degree of reaction, off-design performance, temperature and flow coefficients, surge and rotating stall, stage stacking, non-dimensional parameters of a compressor, phenomena at off-design regimes of a compressor, axial turbines, engine equilibrium running line.

Teaching methods

The module will be delivered primarily through large-class lectures introducing the key concepts and methods, supported by a variety of delivery methods combining the traditional and the technological. The content is presented via a combination of slides, whiteboard and visualiser.

Learning will be reinforced through tutorial question sheets and online exercises, making use of interactive web applications developed specifically for the module, namely the Thermodynamics Cycle Comparison Tool, The Turbofan Calculator, The Supersonic Intake Exercise Tool, and The Compressor Cascade Visualisation and Calculation Tool, featuring analytical tasks representative of those carried out by practising engineers.

Assessments

This module presents opportunities for both formative and summative assessment.  
You will be formatively assessed through progress tests and tutorial sessions. 
You will have additional opportunities to self-assess your learning via tutorial problem sheets. 
You will be summatively assessed by a written examination at the end of the module. 
 
Assessment type Assessment description Weighting Pass mark
Examination Written examination 100% 40%

You will receive feedback on examinations in the form of an examination feedback report on the performance of the entire cohort.
You will receive feedback on your performance whilst undertaking tutorial exercises, during which you will also receive instruction on the correct solution to tutorial problems.
Further individual feedback will be available to you on request via this module’s online feedback forum, through staff office hours and discussions with tutors.

Reading list