Sub-idle is a very challenging operating region, as the performance of a gas tur¬bine engine changes significantly compared to design conditions. In addition, the regulations for new and existing engines are becoming stricter and the prediction of engine’s relight capability is essential. In order to calculate the sub-idle performance of an engine, detailed component representation is required. The data obtained from rig tests is usually insufficient at the low speeds. This creates the need for further research about component behavior within the sub-idle regime before any whole engine relight performance prediction is attempted. Within this research, the sub-idle compressor map generation methodologies are pushed a step forward by the definition of the zero-speed curve, that is the low¬est speed line of a compressor map. In this way the sub-idle characteristic can be interpolated between the zero-speed line and the above-idle given speed lines. Con¬sequently, the generation of the characteristic within the whole range of operation is allowed. In addition, the sub-idle and relight combustion modelling is enhanced by a novel combustion model which accounts for fuel evaporation effects. The de¬velopment of such a model is based on the fact that fuel evaporation effects have a significant impact on the combustion efficiency during the engine relight manoeu¬vres. Finally, the sub-idle exhaust mixing phenomena are investigated as the relight modelling of a mixed exhaust engine cannot be carried out using the conventional approaches as there is a non-negligible difference between the pressures of the two coaxial jets. The models generated by the component related research are partially integrated within the relight performance simulation solver BD19 in order for whole engine performance simulations to be carried out. More specifically, the windmilling and the groundstarting performance of a modern, civil, high bypass ratio engine is examined. The current thesis contributes to knowledge both at component as well as at whole engine performance prediction levels. As far as sub-idle compressor perfor¬mance is concerned, a generic pressure loss model for compressors operating at highly negative incidence angles has been developed. It is validated against experimental data and is applicable on every compressor with given design parameters. In addi¬tion, the new combustion model allows for a more accurate combustion efficiency prediction during the relighting processes while the research on mixed exhaust en¬gine configurations enhances the physical background of the sub-idle mixing process allowing for a more efficient performance modelling. The physics based component related research, in overall, offers significant benefits to the sub-idle and relight per-formance modelling of gas turbines increasing its predictive capability and therefore the reliability of the current and future aero engines.

The non-linear parabolized stability equations (NLPSE) are implemented in a hybrid model for studying noise from round jets. The NLPSE computes instability waves in the flow that may interact nonlinearly to produce noise. This mechanism for noise generation is believed to be a significant contributor to low-frequency noise from subsonic round jets. The NLPSE code has been validated against direct numerical simulation (DNS) data for a number of model problems and the suitability of the method for modelling jet flows has been studied by comparing the results with D S. Near-field results show good qualitative agreement with the DNS. However, the LPSE over predicts the magnitude of near-field fluctuations, which degrades the quality of the final sound-field prediction. It is found that the NLPSE results are highly dependent on the rate of divergence (non-parallelism) of the mean-flow and that a certain amount of eo-flow is necessary to stabilise the downstream-marching numerical scheme for solving the NLPSE. Changing the Mach number confirmed that the NLPSE is very well suited for supersonic jet studies but has difficulty resolving low Mach number jets. It is found that hot jets are also numerically difficult to resolve because the magnitudes of the instability waves increase greatly as the temperature is increased. A linearised Euler equation (LEE) code has been adapted to the round jet problem and found to be an accurate tool for obtaining the sound field from sources defined in the near-field of the jet. By including sources into this code, a LPSE-LEE hybrid code has been implemented, with the LEE part validated against DNS by using modelled near-field sources. Use of this new approach has shown that much can be learnt about the behaviour of jets and the parameters that influence the noise they produce.

No description available.

No description available.

The vibration of turbomachinery blades is an important phenomenon to understand, observe and predict and is the reason for developing a tip timing measurement system. Vibration leads to High Cycle Fatigue (HCF), which limits blade durability and life. HCF can result in blade failure, having expensive consequences for the engine involved. The traditional method for monitoring blade vibration under test conditions is to use blade mounted strain gauges. However, strain gauges are costly and time consuming to install. They have a limited operating life as they are subjected to the harsh on-engine conditions. Only a limited number of blades can be monitored with strain gauges as the number that can be used is limited by the number of channels in the slip ring or telemetry. They can also interfere with the assembly aerodynamics. Consequently non-intrusive alternative techniques such as tip timing are sought. Capacitance probe based clearance measurement systems see widespread use in turbomachinery applications to establish rotor blade tip clearance. This thesis reports investigations into an alternative and additional use in aero-engine rotor blade tip timing measurement for these commercially available systems. Tip clearance is of great importance in the gas turbine industry; this is clear from the fact that gas turbine efficiency has an inverse relationship with tip clearance. Large tip clearance leads to large leakage flows, hence low efficiency, thus the common use of the capacitance probe clearance measurement technique in monitoring turbomachinery. Optical systems have been successfully used to measure rotor blade tip timing on test rigs with several optical probes mounted equally spaced around the turbomachine casing. However, there are practical problems associated with mounting such monitoring systems on in-service jet engines. Optical probes require high maintenance to keep the lenses clean, probably incorporating a purge air system to keep the lenses from fouling. Such impracticalities and added weight make it unlikely that an optical probe based tip timing system will be fitted on an in-service engine in the foreseeable future. In this thesis the scope for a dual use sensor to measure both turbomachinery tip clearance and tip timing is investigated. Since it is impractical to measure blade tip clearance with an optical probe, then the obvious choice for such a sensor is a capacitance probe. Therefore, a commercially available FM capacitance probe based blade tip clearance measurement system is used in a series of tip timing practical investigations. The equipment and instrumentation designed, assembled and produced to facilitate this investigation is documented. These include the development of an optical once per revolution sensor and the design of an independent vibration measurement system based on blade mounted strain gauges. Through an extensive body of experimental work the practicalities in this alternate use of the tip clearance measurement equipment have been assessed. System responses pertaining to tip timing measurement have been investigated, characterised and quantified. The accuracy by which tip timing can be measured using the system has been reported through the findings of an experimental programme carried out on a full-sized, low-speed compressor. Specifically, dual capacitance probe tip timing derived vibration amplitudes have been compared to those derived from blade mounted strain gauge signals. Sources of error have been identified and quantified. Amplitudes were found to agree within the calculated error bands. Instantaneous resonant blade vibrations measured through single capacitance probe tip timing have been correlated with strain gauge derived vibration levels. This has also been done as the rotor traverses blade resonant speed. In this case the vibration phase change across resonance expected from theory was successfully detected through tip timing. Also, the accuracy by which blade time of arrival can be determined by using capacitance probe tip timing has been assessed using a precision OPR sensor and a non-vibrating compressor rotor blade. The characteristics of a DC capacitance probe based clearance measurement system's response to movement in 3D space in proximity to a blade tip have been mapped. Detection of small vibrations have also been investigated in a series of static impulse tests.

No description available.

A gas turbine disc has three critical regions for which lifing calculations are essential: the assembly holes or weld areas, the hub region, and the blade-disc attachment area. Typically, a firtree joint is used to attach the blades to the turbine disc instead of a dove-tail joint, which is commonly used for compressor discs. A firtree joint involves contact between two surfaces at more than one location which makes the joint more difficult to design. Large loads generated due to the centrifugal action of the disc and associated blades are distributed over multiple areas of contact within the joint. All of the contacts in a firtree joint are required to be engaged simultaneously when the blades are loaded. However, slight variations in the manufacture of these components can have an impact on this loading. It is observed that small changes in the geometric entities representing contact between the two bodies can result in variations in the stress distribution near contact edges and the notch regions. Even though manufacturing processes have advanced considerably in the last few decades, the variations in geometry due to these processes cannot be completely eliminated. Hence, it is necessary to design such components in the presence of uncertainties in order to minimise the variation observed in their performance. In this work, the variations in geometry due to the manufacturing processes used to produce firtree joints between a gas turbine blade and the disc are evaluated. These variations are represented in two different ways using measurement data of firtree joints obtained from a coordinate measuring machine (CMM): (i) the variation for the pressure angle in the firtree joint is extracted from a simple curve fit and (ii) using the same measurement data, the unevenness of the pressure surfaces is represented using a Fourier series after filtering noise components. A parametric computer aided design (CAD) model which represents the manufacturing variability is implemented using Siemens NX. Non-smooth surfaces are also numerically generated by assuming the surface profile to be a random process. Two- and three-dimensional elastic stress analysis is carried out on the firtree joint using the finite element code, Abaqus and the variations observed in the notch stresses with changing pressure angle are extracted. A surrogate assisted multiobjective optimisation is performed on the firtree joint based on the robustness principles. Kriging based models are used to build a surrogate for notch stresses and the non-dominated sorting genetic algorithm-II (NSGA-II) is implemented to perform a multiobjective optimisation in order to minimise the mean and standard deviation of the notch stresses. An iterative search algorithm that updates the Kriging models with equally spaced infill points from the predicted Pareto front is adopted. Finally, a new design of the firtree joint is obtained which has better performance with respect to the variation in the notch stresses due to manufacturing uncertainties.

In 1937 the Manchester Engineering Firm Metropolitan Vickers (Metrovick) were awarded a development contract by the Air Ministry to develop a gas turbine for aircraft propulsion in conjunction with the Royal Aircraft Establishment at Farnborough. Over the next decade and a half, the company developed a number of gas turbine designs for a variety of applications in the air, at sea, and on land. This thesis examines the gas turbine work of Metropolitan Vickers, and how the company interacted with a variety of partners across both the military and the civilian realms. These included government research establishments such as the Royal Aircraft Establishment and the Admiralty Engineering Laboratory; commercial partners, such as the aero-engine manufacturer Armstrong Siddeley, Yarrow Shipbuilders, and the Great Western Railway, and state institutions such as the Ministries of Aircraft Production and Fuel and Power. It argues that Metrovick’s technical style was formed by the company’s existing heavy engineering plant business, which privileged design over development and production engineering. Compared to competitors such as Power Jets and Rolls Royce, Metrovick’s progress on aero-engine work was hampered by the lack of a development organisation; though technically advanced, its aircraft engines took a long time to be developed and would not reach production; a factor which was influential in the post-war sale of Metrovick’s aero-engine designs to Armstrong Siddeley. Metrovick did use its gas turbine experience to gain post-war contracts for both naval and civilian gas turbines. The Royal Navy adopted gas turbines for two roles: as lightweight powerplants for short-ranged fast-attack craft, and as part of major warship propulsion systems that were intended to overcome the perceived flaws of the Navy’s interwar steam plants. Metrovick was selected as a development partner because of the company’s existing naval business, as well as its gas turbine expertise. In the civilian realm, the company produced gas turbines for a wide range of applications ranging from railway locomotives to electrical power generation. Most of the customers for these designs were state or quasi-state institutions; this thesis argues that the postwar British state’s support for the civilian gas turbine shows that it was seen as a crucially British technology that could help improve industrial efficiency, as well as utilising indigenous energy resources. However, again Metrovick was content to rely on development contracts rather than commit itself to large-scale production. The company’s gas turbine designs were somewhat marginal to the wider heavy electrical business, and Metrovick never committed the kind of development resources to the gas turbine division that would have been required to produce successful products, nor did it attempt to sell its designs widely to relevant markets.

Low-emissions combustor design is crucially important to gas turbine engine manufacturers. Unfortunately, many designs are susceptible to unsteady oscillations that can result in structural fatigue and increased noise. Computational approaches that resolve flow unsteadiness, for example Large Eddy Simulation (LES), are being explored as one avenue to help understand such phenomena. However, in order to quantifY the accuracy of LES predictions, benchmark validation data in suitably chosen test cases are required. Comprehensive experimental data covering both time-averaged and timeresolved features are currently scarce. It was the aim of this thesis, therefore, to provide such data .in a configuration representing the near-field of a typical gas turbine fuel injector. It was decided to focus on the fuel injector since many unsteady events are believed to originate because of the transient interactions between the fuel injector flow and the main combustor flow. A radial fed two-stream fuel injector, based on a preexisting industrial gas-turbine Turbomeca design was used, since this geometry was known to be susceptible to unsteadiness. The fuel injector was investigated under isothermal conditions to place emphasis on the fluid mechanical behaviour of the fuel injector, including detailed capture of any unsteady phenomena present. Light Sheet Imaging (LSI) systems were used as the primary experimental technique to provide high quality spatially and temporally resolved instantaneous velocity and scalar field information in 2D planes (using ParticieImage Velocimetry (PIV) and Planar LaserInduced Fluorescence (PUF) techniques). Several methods were employed to extract information quantifYing the flow unsteadiness and improve visualisation of timedependent large-scale turbulent structures. Proper Orthogonal Decomposition (POD) analysis enabled clear identification of the dominant modes of energy containing structures. The results indicated that periodic high-energy containing vortex structures occurred in the swirl stream shear layer, emerging from the fuel injector. These formed a two-strong two-weak rotating vortex pattern which propagated down the main duct flow path. The formation of these vortices was found to be a function of the swirl number and originated due to an interaction between the forward moving swirl flow and the furthest upstream penetration point ofthe recirculation zone present in the main duct flow. Dependent on the magnitude of the swirl number (influencing the swirl stream cone angle) and the geometry of the fuel injector, the vortex formation point was sometimes found inside the fuel injector itself. If the vortices originated inside the fuel injector they appeared much more coherent in space and time and of higher energy. A second unsteady high energy containing phenomenon was also identified, namely a Precessing Vortex Core (PVC), which was damped out if the fuel injector contained a central jet. The dynamics of the PVC interacted with the dynamics of the swirl stream shear layer vortices to reduce there strength. Transient scalar measurements indicated that there was a clear connection between the unsteady vortex pattern and the rate of mixing, resulting in bursts of high heat release and is therefore identified as one source of combustor oscillations. Future fuel injector designs need to pay close attention to these unsteady features in selecting swirl number and internal geometry parameters.