Use of Endwall Contouring to Improve the Efficiency of Gas Turbines

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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.