Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

This proposal is in the EPSRC portfolio research area of fluid dynamics and aerodynamics (maintained) and will contribute to the experimental capability and measurement instrumentation knowledge base of the science community. The primary industrial impact of the research will be improvement in energy efficiency, which is one element of the EPSRC energy theme. The gas turbine engine is an adaptable source of power and has been used for a wide variety of applications, ranging from the generation of electric power and jet propulsion to the supply of compressed air and heat. Competition within the industry and, more recently, environmental legislation from government have exerted pressure on engine manufacturers to produce ever more cleaner and efficient products. The most important parameter in governing engine performance and life cycle operating costs is the overall efficiency. High cycle efficiency depends on a high turbine entry temperature and an appropriately high pressure ratio across the compressor. The life of turbine components (vanes, blades and discs) at these hot temperatures is limited primarily by creep, oxidation or by thermal fatigue. It is only possible for the turbine to operate using these elevated mainstream gas temperatures (as hot as 1800 K) because its components are protected by relatively cool air (typically 800 K) taken from the compressor. However, this cooling comes at a cost: as much as 15-25% of the compressor air bypasses combustion to provide the required coolant to the combustor and turbine stages. Ingress is one of the most important of the cooling-air problems facing engine designers, and considerable international research effort has been devoted to finding acceptable design criteria. Ingress occurs when hot gas from the mainstream gas path is ingested into the wheel-space between the turbine disc and its adjacent casing. Rim seals are fitted at the periphery of the system, and a sealing flow of coolant is used to reduce or prevent ingress. However, too much sealing air reduces the engine efficiency, and too little can cause serious overheating, resulting in damage to the turbine rim and blade roots. It is proposed to build a new fully-instrumented rotating-disc rig to measure the flow structure and heat transfer characteristics of hot gas ingress in an engine-representative model of gas-turbine wheel-spaces. An annular single-stage turbine will create an unsteady circumferential distribution of pressure, which in turn will create the ingestion of hot air in the wheel-spaces. The rig will be designed specifically for optical access, with transparent rotating and stationary discs coated with thermochromic liquid crystal and illuminated by a strobe light synchronised to the disc frequency. This will be a new, bold application of the advanced thermal-imaging technology developed at Bath and will provide both qualitative 'thermal visualisation' and quantitative measurements of heat transfer coefficient in the regions on the rotating and stationary surfaces affected by ingress. Miniature unsteady pressure transducers, pressure taps, pitot tubes, fast-response thermocouples and concentration probes will also be used inside the seal annulus and in the upstream and downstream wheel-spaces. In parallel with the experimental programme, new theoretical models developed at Bath will be used extensively in the analysis and interpretation of the experimental data obtained from the new rig. These generic models will be of use to any gas turbine manufacturer, and here this will be demonstrated by specifically translating them into the engine-design methodology used at Siemens. The research will generate unique and practically-useful data which can be rapidly exploited. The successful completion and implementation of this research through improved secondary air system design should result in a competitive advantage for the UK-based company.

Combustion instability is characterized by large-amplitude pressure fluctuations in combustion chambers, and it presents a major challenge for the designer of high-performance, low-emission energy systems such as gas turbines. The instability arises due to complex interactions among acoustics, heat release and transport, and hydrodynamics, which occur over a huge span of time/length scales. In the past, various aspects of the interaction were modelled in isolation, and often on an empirical basis. Advanced mathematical techniques, matched asymptotic expansion technique and multiple-scale methods, provide a means to tackle this multi-physical phenomenon in a self-consistent and systematical manner. By using this approach, a first-principle flame-acoustic interaction theory, valid in the so-called corrugated flamelet regime, has been derived recently. The reduced system in the theory ratains the key mechanisms of combustions instability but is much more tractable computationally. In the present proposed project, the flame-acoustic interaction theory will be extended first to account for the influence of a general externally imposed perturbation. A more general asymptotic theory will be formulated in the so-called thin-reaction-zone regime. Numerical algorithms to solve the asymptotically reduced systems will be developed. The asymptotic theories and numerical methods provide, in principle, an efficient tool for predicting the onset of combustion instability. The fidelity of this approach will be assessed by accurate direct numerical simulations (DNS). It will be applied to the situations pertaining to important experiments in order to predict a number of remarkable phenomena, such as self-sustained oscillations, flame stabilization by pressure oscillations, parametric instability induced by pressure and/or enthalpy fluctuations and onset of chaotic flames. The theoretical models will be employed to develop effective active control of combustion instability by modulating fuel rate, and the effectiveness and robustness of the controllers designed will be tested by simulations using the asymptotic models as well as the fundamental equations for reacting flows.

The gas turbine engine is an adaptable source of power and has been used for a wide variety of applications, ranging from the generation of electric power and jet propulsion to the supply of compressed air and heat. Competition within the industry and, more recently, environmental legislation from government have exerted pressure on engine manufacturers to produce ever more cleaner and efficient products.The most important parameter in governing engine performance and life cycle operating costs is the overall efficiency. High cycle efficiency depends on a high turbine entry temperature and an appropriately high pressure ratio across the compressor. The life of turbine components (vanes, blades and discs) at these hot temperatures is limited primarily by creep, oxidation or by thermal fatigue. It is only possible for the turbine to operate using these elevated mainstream gas temperatures (as hot as 1800 K) because its components are protected by relatively cool air (typically 800 K) taken from the compressor. However, this cooling comes at a cost: as much as 15-25% of the compressor air bypasses combustion to provide the required coolant to the combustor and turbine stages. Ingress is one of the most important of the cooling-air problems facing engine designers, and considerable international research effort has been devoted to finding acceptable design criteria. Ingress occurs when hot gas from the mainstream gas path is ingested into the wheel-space between the turbine disc and its adjacent casing. Rim seals are fitted at the periphery of the system, and a sealing flow of coolant is used to reduce or prevent ingress. However, too much sealing air reduces the engine efficiency, and too little can cause serious overheating, resulting in damage to the turbine rim and blade roots. It is proposed to build a new rotating-disc rig to measure the flow structure and heat transfer characteristics of hot gas ingress in an engine-representative model of a gas-turbine wheel-space. The rig will feature generic engine geometries; it will be fully-instrumented and specifically designed for optical access. An annular, single-stage turbine will create an unsteady circumferential distribution of pressure, which in turn will create the ingestion of hot air in the wheel-space. Fast-response thermocouples and thermochromic liquid crystal in conjunction with a stroboscopic light will be used in thermal transient experiments to measure the temperature of the rotating disc, the stator and the air inside the wheel-space of the rig. Miniature pressure transducers, pressure taps, pitot tubes, and concentration probes will also be used inside the seal annulus and in the wheel-space. In addition, a theoretical model of ingress will be developed and validated using the experimental data collected. This ingress model will be used to obtain correlations of cooling effectiveness and surface temperatures. More generally, the research will provide fundamental insight into the thermal effects of ingress in gas turbines and in turn inform the design of internal air systems.

This project aims to develop an efficient Scalar Dissipation Rate (SDR) based reaction rate closure for the Large Eddy Simulation (LES) of turbulent premixed flames. Although SDR based closures are well established for Reynolds Averaged Navier Stokes (RANS) simulations of non-premixed flames, they are rare for RANS and LES of turbulent premixed flames, and no detailed evaluation of their performance in LES is available so far. In this project, the SDR based reaction rate closures will be developed and simultaneously assessed by a-priori analyses of explicitly filtered Direct Numerical Simulation (DNS) data, and a-posteriori evaluations of model performances in LES calculations, in a configuration for which experimental data is available. Based on the simultaneous a-priori and a-posteriori analyses, new models will be developed and their performance will subsequently be assessed. The best models will then be implemented in a LES code for turbulent premixed flame modelling. An efficient SDR-based reaction rate closure will provide a robust CFD based design tool for reliable, cleaner and cost-effective combustion devices operating in lean premixed mode (e.g. Spark Ignition engines, Lean Premixed Pre-vaporised (LPP) industrial gas turbine combustors).