Investigation of efficient film cooling configurations in realistically turbulent main flow

未来低排放燃气轮机燃烧室的发展需要高效的冷却概念，这种概念允许广泛的选择来控制燃烧过程，因为冷却空气的消耗最小。应用新的冷却配置，如沟槽冷却，其中来自喷口的冷却空气横向分布，所产生的气膜冷却效率可以比简单的喷雾冷却显著提高一个数量级。到目前为止，测量是在主流湍流强度Tu=1%的情况下进行的。当沟槽几何形状暴露在真实燃烧室的较高湍流水平下时，由于冷却空气从表面的提升和与主流的过早混合，冷却效率可能会降低。拟议的研究项目的主要目标是通过实验和数值研究，加深对与沟槽气膜冷却结构相比，在流动冷却中发生的详细流动和换热现象的物理理解。重点研究了实际燃气轮机燃烧室内具有高湍流特性的主流中的冷却油膜。本文将通过实验和数值方法研究主流湍流增强对复杂的非定常流动、混合和换热过程的影响，以及由此产生的换热系数和气膜冷却效率。实验研究将采用光学非侵入式测量技术。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。结合红外和磷光测量技术测量温度边界条件，可以确定局部换热系数的分布。将热像仪高速PIV应用到气膜冷却装置中，可以同时测量流场中温度和速度的时间分辨分布。这使得对复杂的非定常流动结构和湍流通量进行了详细的检查。利用商用CFD软件Ansys Fluent和Realizable k-epsilon模型对实验过程进行了CFD模拟。为了对大涡对薄膜结构和湍流混合的影响进行详细的数值研究，将使用开源CFD程序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.