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

燃烧室冷却概念未来的燃气轮机燃烧室必须在最大冷却效率的情况下使用最少量的冷却空气。在使用低排放稀薄燃烧技术时，燃油喷射器需要大部分空气，同时为了获得最大的燃气轮机工艺效率，热燃气温度不断上升。当使用渗流冷却时，冷却空气射流上升和气膜冷却效率降低，特别是在高吹风率下，这是燃气轮机燃烧应用的典型情况。在像沟槽冷却这样的新型冷却结构中，来自射流的冷却空气是横向分布的，这种提离效应大大减小，在某些操作条件下可以使气膜冷却效率显著提高一个数量级。本研究项目的目标是通过实验和数值研究相结合的方法，更深入地了解与沟槽气膜冷却结构相比，在沟槽冷却结构中发生的详细流动和换热现象。重点是对沟槽冷却结构中复杂的非定常流动、混合和换热过程的研究，这些过程还没有被很好地理解。利用生成的结果，可以开发出优化的气膜冷却装置，其特点是在最小限度地使用冷却空气的情况下，具有均匀且坚固的冷却膜。实验研究将使用光学非侵入性测量技术(PIV-PIV、红外测温、温度敏感颜色-TSP)，辅以热线和热电偶测量。通过使用高速PIV，可以更详细地研究复杂的非定常流动结构。采用红外和TSP测量技术相结合的方法来测量壁面热流，可以确定壁面换热系数的局部分布。伴随实验的CFD模拟使用商业CFD程序(Fluent with Realizable k-epsilon模型)进行。对于大尺度非定常流动结构的详细数值研究，将使用开放源代码的CFD程序OpenFOAM进行大涡模拟，该程序已在研究所建立。

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.