Experiments on Combustor Effusion Cooling Under Conditions of Very High Free-Stream Turbulence

Full-coverage or effusion cooling is commonly used in the thermal management of gas turbine combustion systems. The combustor environment is characterised by highly turbulent freestream flow conditions and relatively large turbulent length scales (length scale-to-coolant hole diameter ratios in excess of 30) that are primarily created by the fuel injector and dilution jets; indeed, the available evidence suggests that large energetic eddies interact strongly with the coolant flows and may have a significant impact on the film-cooling performance. The desire to create compact low-emission combustion systems for aero gas turbine engines has also given rise to a desire to reduce the quantity of air used in wall cooling, and has led to the need for improved thermal design approaches, cooling correlations and validated computational methods. In order to establish a greater understanding of effusion cooling under conditions of very high freestream turbulence, a new laboratory-based test facility has been created that is capable of simulating representative combustor flow conditions, and that allows for a systematic investigation of film-cooling performance over a range of freestream turbulence conditions and coolant to mainstream density ratios. This paper describes the new test facility and its capabilities, including the method for generating combustor relevant flow conditions. Adiabatic film-cooling effectiveness data obtained at a range of blowing ratios are also presented for a typical combustor effusion cooling geometry that uses a twenty degree injection angle. The analysis of this data is supported by fluid temperature field measurements which are presented for low and high freestream turbulence conditions. The interpretation of the data has established the impact of turbulence intensity and integral length scale on the mixing processes between freestream and coolant flows.