Use of Endwall Contouring to Improve the Efficiency of Gas Turbines

燃气轮机技术的发展导致了涡轮入口温度的大幅度提高。这可以提高发动机的功率和效率，但是涡轮入口温度远远超过即使是最先进的材料和涂层的材料能力。采用了一种冷却系统，从发动机的早期压气机阶段排出相对较冷的空气，并将其用作高温高压涡轮阶段的冷却剂。这种冷却空气允许高涡轮入口温度，但发动机效率的提高是有限的，因为冷却液流动导致空气动力学损失，因为它与主流，热气体路径相互作用。当冷却液从涡轮动静轮空间流出时，会产生二次流特征，造成涡轮级的气动损失。这些特征可以通过使用端壁轮廓（EWC）来控制。涡轮端壁是叶片的一部分，通常形成轴对称圆柱体。EWC是涡轮端壁的非轴对称几何形状，用于控制二次流特性，但尽管如此，EWC通常是在没有冷却剂流动的情况下设计的。最近的研究表明，随着吹扫流的引入，EWC的效率增益可能完全丧失。一种组合设计方法是必要的，其中涡轮轮缘密封和EWC是在冷却剂流动的情况下设计的。凭借这种设计方法，以及通过更高效的燃气轮机生产更绿色能源的最终目标，巴斯大学涡轮机械研究中心（TRC）获得了一项研究资助，用于设计和建造一个最先进的燃气轮机测试设施。该设施是与西门子合作设计和建造的，专门用于光学测量技术，如体积三分量粒子图像测速（V3V）。在这些高度不稳定和复杂的流动中，这允许前所未有的细节水平。本博士将实验模拟涡轮与EWC的流动相互作用，这可能会使用V3V进行研究。这是V3V技术的一种新应用，该技术从未应用于涡轮机械的流动。在燃气轮机上采用涡轮轮缘密封和冷却液流动的EWC设计是本项目的首创。利用一个可以穿越涡轮通道、测量速度和压力的气动探头来研究这一阶段的效率。这两种测量技术的结合可以用来了解二次流特征与一次气路相互作用造成的损失。作为该项目的成功成果，预计将获得0.5% - 1%的一级气动效率增益。优化的EWC设计将是下一代燃气轮机设计的关键，可以提高燃油效率并减少燃油消耗。

The development of gas turbine technology has led to a large increase in turbine entry temperature. This allows for engines of increased power and efficiency, however the turbine entry temperatures far exceed the material capabilities of even the most advanced materials and coatings. A cooling system is adopted in which relatively cool air from earlier compressor stages of the engine is bled off and used as a coolant for the hot, high pressure turbine stages. This coolant air allows for the high turbine entry temperatures, but engine efficiency gains are limited as the coolant flow causes aerodynamic losses as it interacts with the mainstream, hot gas path.When the coolant flow egresses from the turbine rotor-stator wheelspace, secondary flow features are generated, causing aerodynamic losses of the turbine stage. These features may be controlled through the use of endwall contouring (EWC). The turbine endwall is the section of the blades that typically forms an axisymmetric cylinder. EWC is a non-axisymmetric geometric shaping of the turbine end wall, and has been used to control secondary flow features, but despite this, EWC is usually designed in the absence of coolant flow. Recent research has shown that the efficiency gains from EWC can be completely lost with the introduction of purge flows. A combined design approach is necessary, where turbine rim-seals and EWC are designed in the presence of coolant flows. With this design approach, and the ultimate aim of producing greener energy through more efficient gas turbines, the University of Bath Turbomachinery Research Centre (TRC) was awarded a research grant to design and build a start-of-the-art gas turbine test facility. The facility, in collaboration with Siemens, was designed and built specifically for optical measurement techniques such as Volumetric Three Component Particle Image Velocimetry (V3V). This allows for unprecedented levels of detail in these highly unsteady and complex flows. This PhD will experimentally model the flow interactions in the turbine with EWC which may be investigated using V3V. This is a novel application of the V3V technique, which has never been applied to flows in turbomachinery. The application of EWC design with turbine rim seals and coolant flows in gas turbines is original to this project.The efficiency of the stage with be investigated using an aerodynamic probe that can traverse the turbine passage, measuring velocities and pressures. The combination of these two measurement techniques may be used to understand the losses caused by the interactions of the secondary flow features with the primary gas path. A 0.5% - 1% stage aerodynamic efficiency gain could be expected as a successful outcome to this project. Optimised EWC designs will be key to the next generation of gas turbine design, increasing fuel efficiencies and reducing fuel burn.