Experimental Measurements of the Effect of Hot Gas Ingestion on Rotor Discs

Project: Research council

Description

The highly adaptable gas turbine engine is one of the most frequently utilised sources of power in the modern age. Derivatives exist in applications ranging from the generation of electric power and jet propulsion to the supply of compressed air and heat. The world market today is driven by increasing fuel costs and reducing CO2 emissions brought about from new environmental legislation. Competition within the industry and the external pressure from government has compelled 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 cycle efficiency. High efficiency depends on a high turbine inlet temperature and an appropriately high pressure ratio across the compressor. In order for elevated mainstream gas temperatures (can be as high as 1800 K) to be viable, the turbine components must be protected from these temperatures, far above their metallurgical limit. Relatively cool air (typically around 800 K) bled from the compressor is used to extend the life of these turbine components, which would otherwise be limited by creep, oxidation or by thermal fatigue. However, cooling air is expensive: approximately 20% of the compressed air is used for cooling and not combustion. Effective use of the cooling air is therefore key to designing an efficient gas turbine. One of the most important cooling-air problems facing gas turbine designers today is the ingestion of hot mainstream gases into wheel-spaces between the turbine discs and their adjacent casings. 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 (with an associated increase in fuel consumption and CO2 emissions), and too little can cause serious overheating, resulting in damage to the turbine rim, blade roots and disc: the correct sealing balance is therefore of critical importance. A recently completed experimental programme (funded in part by EPSRC grant EP/G096107/1) has successfully modelled ingestion into a single-stage gas turbine (referred to here as the 'single-stage facility'). The programme had great success both in terms of industrial impact and academic publication, improving the design of gas turbine rim seals through extensive experimental measurements made on the stationary turbine disc (stator) and in the wheel-space between the discs. This new research will build on the previous achievements by transforming the single-stage facility to allow for experimental heat transfer measurements to be made on the rotating disc (rotor). Surface temperatures measured in a transient experiment using new infra-red technology will be used in conjunction with new specifically developed analysis techniques to increase the accuracy of adiabatic wall temperature measurements. The data will directly lead to adiabatic sealing effectiveness distributions on the rotor. The experiments, which would be conducted under fluid dynamic conditions representative of those found in engines, will lead to crucially important rotor metal temperatures at engine operation conditions for use by the designer. This would be a world first: many research workers have measured the minimum coolant flow rate necessary to prevent ingress using measurements on the stator, but no one has simultaneously measured the heat transfer from the gas to the rotating turbine disc after the gas has entered the wheel-space. As a result of the successful completion of this experimental research, an extensive database of rotor disc heat transfer data will be used to improve the design of gas turbine secondary air systems at Siemens. The UK-based company will receive a competitive advantage, both in exploiting the practically-useful data generated from the research and also in significantly influencing the 1D design methodology within the company.
StatusFinished
Effective start/end date2/01/141/01/16

Funding

  • Engineering and Physical Sciences Research Council

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Ingestion (engines)
Gas turbines
Turbines
Rotors
Engines
Air
Gases
Cooling
Turbine components
Wheels
Compressed air
Heat transfer
Coolants
Stators
Seals
Compressors
Temperature
Industry
Thermal fatigue
Rotating disks