Unsteady flow effects on film cooling in low-emissions gas turbine combustors

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The strong growth in commercial aviation is set to continue for the foreseeable future. Both the aviation industry and government state that this expansion is only sustainable with the improved environmental performance of the aviation business sector. This is placing pressure on aircraft engine manufacturers to produce cleaner, more efficient products. Most civil airliners are powered by turbofan jet engines. All of the energy input in these engines is introduced by burning fuel in a combustor. The combustor is designed to maximise the heat liberated from the fuel whilst also minimising the generation of pollutants. Gas temperatures in the combustor can be greater than 2000 centigrade and this is well above the melting point of the metal components of the combustor. To stop the combustor from overheating and potentially melting, it must be cooled in some way. This is achieved by using relatively cool air from the engine's compressor which is fed as a film along the surfaces exposed to the hot gases: this is known as film-cooling. The air flow in a combustor is extremely complex, and is highly turbulent. Large vortices pass through the combustor, giving an unsteady flow that periodically rips off the cooling film and exposes the combustor walls to very hot gases. Combustor designers and researchers still do not fully understand the way in which the cooling film is affected by the hot combusting flow, a situation that is hampering efforts to improve performance and achieve emissions targets. Low-emissions combustors use lean-burn technology where more air is mixed with the fuel reduce the flame temperatures. This means that less air is available for cooling the combustor walls.The overall aim of this project is to investigate the fluid dynamics of a low-emission combustor, and to understand how this affects the transfer of heat to the combustor walls. The project will deliver detailed information on how various parameters affect the complex flows. This requires the building of a new wind-tunnel that is specifically designed to simulate the flows in low-emission gas turbine combustors. It will also require the application of advanced techniques such as laser-based flow velocity measurement as well as technologies for measuring the heat transfer to the walls. By using advanced data analysis it will be possible to understand how the unsteady flow-field is interacting with the cooling films and why the heat transfer to the walls is affected. The project will also generate correlations between heat transfer and flow conditions that can be used by engine manufacturers in the design process of new aircraft engines. It will also be used to estimate how cooling technologies will need to perform in the future with new lower emissions combustor designs.This work will be applied in the development of new gas turbine combustion systems. It will benefit engine manufacturers directly. The improved understanding will contribute to better and faster design by manufacturers, reducing the amount of cooling air needed and thereby helping to reduce pollutant emissions. The data produced by the project will help other researchers in the field, particularly those who are looking at computational based investigations of combustor flows. Finally, the contribution of the work towards lower aviation emissions will benefit the public through the reduced environmental impact of the aviation industry.