Flow and heat transfer in complex film cooling configurations for application in future gas turbine combustors

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Combustor cooling concepts for future gas turbine combustors must operate with a minimum amount of cooling air at maximum cooling efficiency. When using the low emission lean combustion technology, most of the air is required in the fuel injector, while at the same time the hot gas temperatures continue to rise in order to obtain maximum gas turbine process efficiency. When using effusion cooling, a liftoff of the cooling air jets and a reduction of the film cooling efficiency occurs especially at high blowing rates, which are typical of gas turbine combustion applications. In new cooling configurations like the trench cooling, where the cooling air from the effusion jet is distributed laterally, this lift-off effect is reduced considerably and can result in a considerably improved film cooling efficiency by one order of magnitude for some operating conditions.The goal of the proposed research project is to develop a deeper physical understanding of the detailed flow and heat transfer phenomena that occur in effusion cooling as compared to trench film cooling configurations by a combination of experimental and numerical investigations. The emphasis will be on the investigation of the complex unsteady flow, mixing and heat transfer processes in trench cooling configurations, which are not well understood. Using the generated results, optimized film cooling devices can be developed which feature a uniform and (for a large range of operating conditions) robust cooling film at minimal use of cooling air.The experimental research will use optical non-intrusive measurement technology (PIV - PIV, infrared temperature measurements, temperature-sensitive colors - TSP), supplemented by hot-wire and thermocouple measurements. Through use of high-speed PIV, the complex unsteady flow structures can be examined in great detail. A novel combination of infrared and TSP measurement techniques for measuring wall heat flows allows the determination of the local distribution of the heat transfer coefficient.The CFD simulations accompanying the experiment are performed using a commercial CFD code (FLUENT with realizable k-epsilon model). For the detailed numerical studies of the large scale unsteady flow structures, large eddy simulations will be performed using the open source CFD code OpenFOAM, which is already well established at the institute.