Investigation of efficient film cooling configurations in realistically turbulent main flow

未来低排放气体涡轮机燃烧器的发展需要有效的冷却概念，由于冷却空气的最小消耗，这允许广泛的选择来控制燃烧过程。应用新的冷却配置，如沟槽冷却，其中来自泻流射流的冷却空气横向分布，与简单的泻流冷却相比，所得到的薄膜冷却效率可以显著提高高达一个数量级。到目前为止，测量是在Tu = 1%的主流湍流强度下进行的。当将沟槽几何形状暴露于真实的燃烧室的较高湍流水平时，冷却效率可能会降低，这是由于冷却空气从表面的上升和与主流的过早混合。拟议的研究项目的主要目标是实现更深入的物理理解的详细流动和传热现象发生在泻流冷却相比，沟槽薄膜冷却配置通过实验和数值研究。重点研究了真实的燃气涡轮机燃烧室内高湍流特性主流中的冷却膜。将采用光学非侵入式测量技术，通过实验和数值计算研究这种主流湍流度的增加对复杂的非定常流动、混合和传热过程的影响，以及由此产生的传热系数和气膜冷却效率。除了LDA和高速PIV等标准技术外，还将优化和应用新的测量技术。利用红外和磷光测量技术的组合测量温度边界条件，可以确定局部传热系数的分布。将热像高速PIV技术应用于气膜冷却装置中，可以同时测量流场的时间分辨温度和速度分布。这使得复杂的非定常流动结构和湍流通量的详细检查。使用商业CFD代码ANSYS Fluent和可实现的k-curve模型进行伴随实验的CFD模拟。对于大涡对膜结构和湍流混合的影响的详细数值研究，将使用开源CFD代码OpenFOAM进行大涡模拟。

The development of future, low emission gas turbine combustors requires efficient cooling concepts, which allow a wide range of options to control the combustion process due to a minimum consumption of cooling air. Applying new cooling configurations like the trench cooling, where the cooling air from the effusion jet is distributed laterally, the resulting film cooling efficiency can be considerably improved by up to one order of magnitude compared to simple effusion cooling. Up to now measurements were conducted at a main flow turbulence intensity of Tu = 1%. When exposing the trench geometry to the higher turbulence level of a real combustion chamber, the cooling efficiency might be reduced due to increased liftoff of the cooling air from the surface and premature mixing with the main flow.The main goal of the proposed research project is to achieve a deeper physical understanding of the detailed flow and heat transfer phenomena that occur in effusion cooling as compared to trench film cooling configurations through experimental and numerical investigations. The focus is on study of cooling films in a main flow of high turbulence characteristic for flows in real gas turbine combustion chambers. The effect of this increased main flow turbulence on the complex unsteady flow, mixing and heat transfer processes, as well as the resulting heat transfer coefficients and film cooling effectiveness will be studied experimentally and numerically.The experimental studies will use optical non-intrusive measurement technology. Besides standard techniques such as LDA and high speed PIV, novel measurement techniques will be optimized and applied. Using a combination of infrared and phosphorescence measurement techniques for measuring temperature boundary conditions, the distribution of the local heat transfer coefficient can be determined. Applying thermographic high speed PIV to the film cooling setup, time resolved simultaneous temperature and velocity distributions in the flow field can be measured. This allows the detailed examination of the complex unsteady flow structures and of the turbulent fluxes. The CFD simulations accompanying the experiment are performed using the commercial CFD code ANSYS Fluent with realizable k-epsilon model. For the detailed numerical studies of the effect of large eddies on the film structure and on the turbulent mixing, large eddy simulations will be performed using the open source CFD code OpenFOAM.