Gas Turbine Engineer Apprenticeship

To inform you of the different types of gas turbine engines; their applications, on-design, off-design and transient performance.

To provide you with the ability to undertake gas turbine component performance calculations, diagnostics and to perform evaluations of gas turbine performance, and deterioration.

Gas Turbine Types and Applications

Effect of design parameters such as pressure ratio and turbine temperature on the basic gas turbine cycle. Modifications of the basic Brayton cycle, compounding, intercooling, reheating, heat exchange, bypass, and fan cycles. Simulation of the above.

Performance and Simulation

Design point performance of turbojet, turbofan and turboshaft cycles, effect of bypass ratio. Off design performance, effect of ambient temperature, altitude, throttle setting and flight speed. Non-dimensional representation. Gas turbine simulation. Effects of bleeds and power offtakes. Compressor turbine matching. Gas turbine degradation. Simulation and diagnostics of the above. Component maps. Surge alleviation, performance improvements, steady-state, and transient performance. Off-design performance calculations and iteration techniques Accelerations, decelerations, effects on surge margin. Transients of single shaft and multi-shaft engines. Transient performance simulation. Effects of heat transfer on transient performance.

Software used for gas turbine performance simulation: TURBOMATCH

Diagnostics and Monitoring.

Description of gas turbine performance degradation and faults.

Description of most used gas turbine condition monitoring techniques.

Software used for diagnostics: PYTHIA

On successful completion of this module you should be able to:

1. 1. Examine the gas turbine components and evaluate the performance in terms of power, thrust and specific fuel consumption of various types of gas turbine engines.
2. 2. Assess the results from quantitative evaluations of gas turbine designs to determine appropriate power or propulsion systems for different applications.
3. 3. Set up numerical iterative methods for the matching of engine components to generate the engine running line.
4. 4. Assess the impact of different degradation and faults on gas turbine performance.
5. 5. Assemble computer based simulation and diagnostic analysis tools to simulate engine performance and detect its faults.

To familiarise you with compressor and turbine aerodynamic design and performance by instruction, investigation and example.

To introduce you to the technology of gas turbine blade cooling through analytical and practical approaches of heat transfer principles, convection cooling, impingement film transpiration cooling and liquid cooling.

Thermofluids: Introduction to aerodynamics, thermofluids, and compressible flows.

Compressor Design and Performance

Overall performance:  Fundamentals of axial flow compressors.  Overall performance, achievable pressure ratio and efficiency. The effect of Reynolds number, Mach number, and incidence. Definition of isentropic and polytropic efficiency, effect of pressure ratio, performance at constant speed, surge and surge margin definitions, running line, choking effects.

The axial compressor stage: Stage loading and flow parameters, limitation in design on pitch line basis. Definition and choice of reaction at design, effect on stage efficiency. Loss sources in turbomachines and loss estimation methods. The ideal and real stage characteristic, stall and choke. The free vortex solution, limitations due to hub/tip ratio. Off-design performance Choice of overall annulus geometry, axial spacing, aspect ratio, limitations of rear hub/tip ratio. Compressor blading: selection of blade numbers, aspect ratio and basic blade profiling.

Compressor design example: Multi-stage compressor design example carried out for a HPC.

Turbine Design and Performance

Overall performance: the expansion process and characteristics, annulus layout and design choices, choice of stage loading and flow coefficient, engine overall performance requirements, overall annulus geometry and layout; rising line, constant mean diameter and falling line.

The axial turbine stage: Aerodynamic concepts and parameters, velocity triangles, reaction, stage loading, flow coefficients. The ideal and real characteristic. Design  for maximum power: effect of choking and change of inlet temperature and pressure.  Stage efficiency, overtip leakage, profile losses, correlations. Three-dimensional design aspects. Radial equilibrium and secondary flows.

Turbine blading: choice of base profile, blade numbers and aspect ratio. Zweiffel's and alternative lift coefficients.

Turbine Design Example: An aerodynamic design example is carried out for a HPT Heat Transfer Principles: Brief review of heat transfer principles and physical significance of non-dimensional groupings. Conditions around blades, boundary layers, external heat transfer coefficient distribution, effect of turbulence. Root cooled blades and NGVs, analytical and numerical methods of determining spanwise temperature distribution. Fibre strengthened and nickel base alloys.

Need for high turbine entry temperature: effect on engine performance.

Development of materials, manufacturing processes and cooling systems.

Convection Cooling: Convectively cooled aerofoils: analytical approach for metal and cooling air spanwise temperature distribution. Cooling passage geometry and heat transfer characteristics. Cooling efficiency, cooling effectiveness and mass flow function: application at project design stage for determining metal and cooling air temperatures. Methods for optimising cooling system design: secondary surfaces and multipass. Internal temperature distribution of cooled aerofoils: calculations, comparisons with experimental results.

Impingement, Film and Transpiration Cooling: Principles steady state and transient performance, characteristics, advantages, limitations, comparison with convection cooling. Cooling air feed and discharge systems. Integration of cooled turbine with aerodynamic performance and main engine design. Co-ordination of design responsibilities. Example of cooled turbine stage design.

Liquid Cooling: Liquid cooling: principles, advantages and limitations, practical examples.

On successful completion of this module you should be able to:

1. 1. Identify and analyse the design and performance characteristics of turbomachinery components.
2. 2. For given inlet conditions and requirements, determine the aerodynamic performance characteristics of a turbomachine and comment on the feasibility of the design.
3. 3. Differentiate the key design choices for axial compressors and turbines, Construct an assessment of the aspects which affect the design and performance of axial turbomachines an apply formulations and critical evaluations of underpinning turbo-machinery theories.
4. 4. Explain the requirement for ethical and professional conduct in the use of data and in the presentation of results and calculations.
5. 5. Explain the major differences between the various heat transfer and cooling architectures and apply the concepts and theories of heat transfer and different cooling technologies to the cooling of turbine blades to produce a realistic assessment of their cooling requirements.

To make you familiar with design, operation, computation and performance criteria of gas turbine (GT) combustion and reheat systems and to explore issues related to gas turbine pollutant emissions.

Introduction to GT combustor design considerations and sizing methodologies:

Diffusion and pre-mixed flame characteristics; GT combustor design features and performance requirements; Design considerations and main functions of the primary, intermediate and dilution zones; Fundamental aspects of the ignition process; Sources of pressure loss; Performance criteria and requirements for pre-combustor diffusers; Faired and dump diffusers; Combustor sizing methodologies based on the pressure loss approach, combustor efficiency requirements and altitude relight requirements.

Combustion efficiency:

Definition of combustion efficiency and combustion efficiency requirements; Evaporation rate controlled systems – influence of fuel type, turbulence and pressure, drop size and residence time; Mixing rate controlled systems; Reaction rate controlled systems – derivation and significance of the “q” parameter.

Overview of GT generated pollutants:

Products of combustion and their consequences; Mechanisms of formation of GT pollutants; Effects on the environment and/or human health; Overview of limitation strategies and associated challenges; Low emissions combustion systems for aero and stationary gas turbines; Emissions legislation and targets.

GT combustor heat transfer and cooling:

Combustor buckling and cracking; Need for efficient methods of liner cooling; Heat transfer processes (Internal and external radiation, internal and external convection, conduction); Calculation of uncooled liner temperature; Effect of chamber variables on heat transfer terms, liner wall temperature and liner life; Film cooling techniques; Advanced wall cooling techniques; Combustor liner materials and thermal barrier coatings.

GT fuels

Appraise types and properties of fuels; Methodologies to calculate combustion temperatures for various fuel types, mixture strengths and pressures (both non-dissociated and dissociated).

Computational methods for GT Combustors

Role of CFD in combustor design and development; Application of CFD for preliminary design, prognostics and diagnostics of combustion systems.

Introduction to GT afterburners:

Requirement and principle of afterburning; Effects of afterburning on engine performance; General arrangement, main components and design features of afterburners; Ignition methods for GT afterburners; Control requirements and methods for engines with afterburners; Considerations for selection of convergent and convergent-divergent nozzles.

On successful competition of this module you should be able to:

1. 1. Explain and evaluate the concepts underpinning the design of gas turbine combustors and reheat systems for both aero and stationary gas turbines, and explain the influence of the design choices on overall engine configuration and performance.
2. 2. Assess the influence of: fuel types and preparation, combustion efficiency, ignition requirements, diffuser performance, operational criteria, pollutant emissions and legislation, cooling and material technology on combustor sizing, design and performance.
3. 3. Apply heat transfer techniques to the calculation of combustor liner temperature and assess the effect of materials, advanced cooling methods and thermal barrier coatings on the life of a combustor liner.
4. 4. Employ methodologies to calculate combustion temperatures for various fuel types, mixture strengths and pressures.
5. 5. Distinguish between simple and more advanced computational methods for combustor performance prediction in terms of their modelling and capabilities.

To familiarise you with the common problems associated with the mechanical design and the lifting of the major rotating components of the gas turbine engine.

Loads/forces/stresses in gas turbine engines: The origin of loads/forces/stresses in a gas turbine engine such as loads associated with: rotational inertia, flight, precession of shafts, pressure gradient, torsion, seizure, blade release, engine mountings within the airframe and bearings. Discussion of major loadings associated with the rotating components and those within the pressure casing including components subject to heating.

Failure criteria: Monotonic failure criteria: proof, ultimate strength of materials. Theories of failure applied to bi-axial loads. Other failure mechanisms associated with gas turbine engines including creep and fatigue. Fatigue properties including SN and RM diagrams, the effect of stress concentration, mean stress etc. Cumulative fatigue, the double Goodman diagram technique to calculate the fatigue safety factor of gas turbine components. Methods of calculating the creep life of a component using the Larson-Miller Time-Temperature parameter.

Applications: The design of discs and blades. Illustration of the magnitude of stresses in conventional axial flow blades by means of a simple desk-top method to include the effects of leaning the blade. The stressing of axial flow discs by means of a discretised hand calculation which illustrates the distribution and relative magnitude of the working stresses within a disc. The design of flanges and bolted structures. Leakage through a flanged joint and failure from fatigue.

Blade vibration: Resonances. Desk top techniques for calculating the low order natural frequencies of turbomachine blades. Allowances for the effects of blade twist and centrifugal stiffening. Sources of blade excitation including stationary flow disturbance, rotating stall and flutter. Derivation of the Campbell diagram from which troublesome resonances may be identified. Allowances for temperature, pre-twist and centrifugal stiffening. Methods for dealing with resonances.

Damage Mechanisms and Lifing: Fundamentals of Creep and Fatigue damage mechanisms. Material, design and operational parameters that affect creep and fatigue. Experimental and test procedures to characterise creep and fatigue damage. Classification of Fatigue-Low Cycle and High Cycle and use of appropriate methods: Strain Vs Stress Methods. Cumulative damage assessment using cycling counting and linear damage rules -Milner Approach.  

On successful completion of this module you should be able to:

1. 1. Describe and distinguish the design requirements and loads encountered by gas turbine components during normal operation.
2. 2. Evaluate and assess the loads, stresses, failure criteria and factors of safety used in gas turbine engines.
3. 3. Evaluate impact of vibrations on design and operation of gas turbine.
4. 4. Assess the creep and fatigue damage of gas turbine components based on design and operational parameters.

• Professor Panagiotis Laskaridis

To enable course members to determine the life cycle of machines and machine components.

In this module it is proposed to introduce students to the problem of lifting machines for repeated (cyclic) loads. Of course, there must also be an awareness of the damage arising from (so-called) steady loads (proof case), and from high temperature (creep case), but without doubt, the most damaging of all the failure modes is fatigue, which arises when a load is applied repeatedly, as when a gas-turbine is operated many times, or when a component, within the gas turbine, vibrates.

It is not intended to dwell on the metallurgic nature of fatigue but instead to introduce students to calculating techniques, some of them quite simple, with which they may be able to determine the probable life of a machine. Fatigue and fracture are simply two sides of the same coin since they both give us insight into the nature of cyclic fracture, and both allow the determination of the cyclic life of a component under certain operating conditions.

Fatigue is essentially empirical in nature that is, based on experience going back to the age when wheels first fell off rolling stock. Fracture is much more analytical in nature, and based upon an analytical model of the small flaw (imperfection) which all failed components can be assumed to have held. The course is liberally sprinkled with worked examples. Emphasis is placed on the application of Fatigue and Fracture theory on aero and stationary gas turbines and their components including turbo-machinery shafts, blades and disks.

Materials: Materials Selection Process, Gas Turbine Materials, Aluminium alloys, Titanium alloys, Nickel and Cobalt superalloys, Metal Matrix Composites, Ceramic Matrix Composites, Polymer Composites, Coatings Technology for gas turbines, Corrosion Resistant Coatings, Thermal Barrier Coatings, Future Gas Turbine Materials.

To familiarise the course member with various operations of gas turbines and other driven rotating machines.

Gas Turbine Operations:
• An overview of the different operational regimes for gas turbine application. This explores base load, peak load, standby and backup operations, alongside their individual operational requirements. It also includes engine control modes such as operating at approximately constant exhaust gas temperature and load-following mode. Analysis of gas turbine performance and health using machine sensor data from actual operation is also a key part. This part also highlights the use and impact of ancillary equipment (air filtration and compressor washing systems) in improving the performance and extending the operating hours of gas turbine machines. Gas turbine operational flexibility for back-up of renewable power.

Steam Turbine Operations:
• Steam turbine fundamentals, applications and selection. This includes an overview of steam turbine plants operating on fossil fuel - combined cycle gas turbines (CCGT) and combined heat and power (CHP) operations. It also covers aspects of heat recovery systems, condensers, pumps and other auxiliary equipment.

Diesel Engines for Heat and Power:
• Diesel engine fundamentals; theory and principles. This includes 2-stroke (crosshead engine) and 4-stroke (trunk piston) types, their installation and operations. Utilisation of diesel engine waste heat recovery for district heating hot water systems, cooling systems using chiller and fresh water generation are the common applications explored. Diesel engine fuels and the means of controlling exhaust emissions are included.

On successful completion of this module you should be able to:

1. 1. Evaluate gas turbine performance using machine data from actual operations.
2. 2. Assess engine performance deterioration, as well as propose improved approaches in enhancing performance during operation.
3. 3. Distinguish and compare key components and parameters and further relate them to steam turbine theory, performance and operation.
4. 4. Differentiate and assess the applications of steam turbines.
5. 5. Calculate diesel engine performance, differentiate between 2-stroke and 4-stroke engines and the operational requirements, also with respect to heat and power.

The importance of technology leadership in driving the technical aspects of an organisation’s products, innovation, programmes, operations and strategy is paramount, especially in today’s turbulent commercial environment with its unprecedented pace of technological development. Demand for ever more complex products and services has become the norm.

The challenge for today’s manager is to deal with uncertainty, to allow technological innovation and change to flourish but also to remain within planned parameters of performance. Many organisations engaged with technological innovation struggle to find engineers with the right skills.

Specifically, engineers have extensive subject/discipline knowledge but do not understand management processes in organisational context. In addition, STEM graduates often lack interpersonal skills.

• Engineers and Technologists in organisations: The role of organisations and the challenges facing engineers and technologies.
• People management: Understanding you. Understanding other people. Working in teams. Dealing with conflicts.
• The Business Environment: Understanding the business environment; identifying key trends and their implications for the organisation.
• Strategy and Marketing: Developing effective strategies; Focusing on the customer; building competitive advantage; The role of strategic assets.
• Finance: Profit and loss accounts. Balance sheets. Cash flow forecasting. Project appraisal.
• New product development: Commercialising technology. Market drivers. Time to market. Focusing technology. Concerns.
• Business game: Working in teams (companies), students will set up and run a technology company and make decisions on investment, R&D funding, operations, marketing and sales strategy.
• Negotiation: Preparation for Negotiations. Negotiation process. Win-Win solutions.
• Presentation skills: Understanding your audience. Focusing your message. Successful presentations. Getting your message across.

On successful completion of this module you should be able to:

1. 1. Recognise the importance of teamwork in the performance and success of organisations with particular reference to commercialising technological innovation.
2. 2. Operate as an effective team member, recognising the contribution of individuals within the team, and capable of developing team working skills in themselves and others to improve the overall performance of a team.
3. 3. Compare and evaluate the impact of the key functional areas (strategy, marketing and finance) on the commercial performance of an organisation, relevant to the manufacture of a product or provision of a technical service.
4. 4. Design and deliver an effective presentation that justifies and supports any decisions or recommendations made.
5. 5. Argue and defend their judgements through constructive communication and negotiating skills.

This module aims to introduce you to aircraft engine control and to explain the philosophy of jet engine control requirements and systems to gas turbine engineers.

Compressor performance
The difficulty of compressing air; the overall compressor characteristic and its graphical presentation. Running line and surge line. Performance limitations at low rotational speed and low airflow. Design for surge alleviation. The use of variable inlet guide vanes, variable stators, air bleed, multi-spooling.

Axial turbine performance
Physics of expanding gas flows and choking. Performance at maximum flow. Effect of changes in inlet temperature and pressure. The turbine overall performance characteristic and turbine efficiency.

Gas turbine control
Needs and Implementation. The gas turbine is a very complex mechanism that has to operate within many constraints including aerodynamic, mechanical and handling issues. At the same time it also needs to be responsive and operate safely. An explanation will be given on these constraints and how different features such as variable stators, bleed valves and variable area nozzles can be used to implement safe and responsive engine handling. An explanation on component matching and the influence of each control feature on the operation of the engine.

Introduction to fuel systems and fuel pumps
To include the role of the fuel system; fuel properties; typical fuel flows, temperatures, and pressures in the system, descriptions of low pressure first stage pump, high pressure second stage pumps; typical modern control systems.

Airframe Fuel Systems
Low Pressure Engine Fuel Systems. To include typical LP system architecture, fuel pump inlet pressure requirements, the concept of Net Positive Suction Pressure (NPSP), establishing the low pressure pump design points; low pressure first stage pump types; fundamentals of LP pump design.

High pressure engine fuel pumps
Difference between positive displacement and rotodynamic pumps, types of positive displacement pumps; selecting the optimum drive speed; sizing a positive displacement pump; the effect of leakage on pump size and heat rejection; mechanical design considerations; journal bearing design; pointing design and minimising cavitation erosion damage.

Hydro-mechanical fuel metering
Brief history of fuel control architectures leading to FADEC systems; Functions required by modern FADEC based fuel controls; impact of reliability requirements on modern fuel control architecture; modern fuel control architecture; basic principles of fuel flow; fuel metering; electrical interface devices used on modern fuel controls; engine actuation; demonstration of modern fuel control hardware; fitness for purpose, future trends in fuel control.

Electronic engine control
To include circuit design, mechanical design, software.

Staged Combustion
To include aircraft emissions, emissions legislation, controlling emissions, fuel control requirements, fuel control, control laws.

Fuel controls for ‘more/all’ electric engines
To include impact of the More/All electric engine on fuel control, positive displacement pump based systems, centrifugal pump based systems, technical challenges.

Airworthiness considerations
European and USA regulatory requirements relevant to certification and substation of engine controls and fuel systems including their installation. Service history, occurrences and case studies.

On successful completion of this module you should be able to:

1. 1. Analyse the control needs and operational issues associated with gas turbines used for aircraft propulsion.
2. 2. Describe and distinguish the objectives of the control philosophies of the available systems.
3. 3. Assess jet engine control systems design as applied to different forms of aircraft propulsion.
4. 4. Evaluate the different mechanisms and components that allow the safe and efficient operation of a jet engine.
5. 5. Examine and analyse regulatory requirements relevant to engine controls and fuel systems.

To equip you with background knowledge of aircraft propulsion, component performance integration.

The course is divided into two major components: Aircraft Engine and Component Performance and System Performance and Integration.

Aircraft Engine and Component Performance
Three main topics are dealt with in this section: Aircraft Performance, Jet Engine Performance, Intakes and Exhaust Systems.

• Aircraft Performance:
Deals with the major topics of flight and aerodynamics, such as lift, drag, range, performance and a section on the design of aircraft for different purposes.

• Jet Engine Performance:
Focuses mainly on the off-design performance of jet engines. Engine behaviour at different altitudes, flight speeds, ambient conditions and throttle settings are described. This topic features a presentation on the design of engines for various types of aircraft.

• Intakes and Exhaust Systems:
Outlines the major design features and operation of the components for subsonic and supersonic aircraft applications.

System Performance and Integration:
This portion of the course starts with the analysis of fundamental aerodynamics of unducted and ducted bodies. This is followed by the development, via the formal definitions of thrust and drag and the concept of stream-tube momentum force, of the relationship between the net propulsive force of the powerplant, engine thrust and nacelle forces. Alternative performance accounting relationships are developed for various choices of thrust interface using force, drag and the hybrid force/drag method. These are employed to illustrate the interplay between component forces. The treatment addresses the long and short-cowl podded nacelles, appropriate to civil engine installations, on- and off-wing; and the highly integrated installations encountered in military aircraft.

On successful completion of this module you should be able to:

1. 1. Analyse and assess aircraft performance in terms of lift, drag and range.
2. 2. Analyse the performance of jet engines over a range of altitudes, flight Mach numbers and spool rotational speeds.
3. 3. Evaluate and assess the various intake and exhaust systems available for different aircraft applications.
4. 4. Compare and differentiate the various engine installation configurations associated with the major aircraft applications.
5. 5. Compare component performance accounting relationships to analyse installation performance in respect of the integration of the engine and airframe.

To introduce you to computationally-based flow modelling, applicable to turbomachinery components and gas turbine engines.

To introduce you to the theoretical background of Computational Fluid Dynamics and to the limitations of CFD when applied to the solution of turbomachinery fluid flow problems. To provide experience in the use of a commercial CFD code through planning and conducting investigations of complex turbomachinery flow cases.

Flow Modelling Strategies
Introduction to computational fluid dynamics and the role of CFD in engine component evaluation and improved design. Review of current capabilities and future directions.

Physical Modelling
Governing Navier-Stokes equations. Approximate forms. Turbulence - turbulent averaging, mathematical closure and turbulence modelling. Scalar transport and chemical reaction. Reynolds averaging, Large Eddy Simulation, Direct Numerical Simulation.

Finite Difference Equations
Problem classification. Discretisation. Solution methods. Pressure correction. Boundary conditions. Mesh generation for practical flow geometries.

Practical Demonstration
Introduction to commercially available general purpose CFD codes (FLUENT and CFX). Case study tutorials and assessed assignment.

On successful completion of this module a you should be able to:

1. 1. Summarise the key steps associated with the CFD modelling approach whilst adhering to good practice in the employment of numerical tools.
2. 2. Design effective turbomachinery grid generation strategies to ensure numerical models are successfully employed.
3. 3. Describe the fundamentals of turbulence modelling when applied to turbomachinery flows.
4. 4. Plan, conduct, analyse and evaluate an engineering fluid problem using a commercial CFD package (Ansys Fluent/CFX).
5. 5. Use CFD tools to generate effective analyses, evaluations and reporting of turbomachinery flow simulations.