It is now widely agreed by the scientific community that global warming is a direct result of human industrialization; and primarily the release of carbon dioxide in to the atmosphere through the burning of fossil fuels. In the United States approximately 20% of greenhouse gas emissions result from the burning of fossil fuels for electrical power generation, of which industrial gas turbines are a major contributor. The 2016 Paris Agreement was the first legally binding agreement between 195 countries which aims to limit global warming and its adverse effects on Earth. This can only be achieved through minimising the adverse environmental impact of products and processes in all aspects of human life.
This PhD research aims to achieve an increase in industrial gas turbine stage efficiency in the order of 1% through the use of novel rotor endwall contouring in the presence of egress purge flow; the endwall being the circumferential platform upon which the rotor blades sit, and egress purge flow being flow entering the main annulus gas path from the wheelspace formed between the rotor and stator. Endwall contouring has the potential to benefit stage efficiency as it can be used to suppress parasitic secondary flow structures found in the rotor blade passage. In the past, research in to the design of endwall contours for this purpose has given little consideration to their performance in the presence of egress purge flow, and recent work has shown that the ability for endwall contours to supress secondary flow structures is highly dependent of the levels of egress purge flow; this PhD aims to fill this important gap in the existing literature. This will be achieved by testing a series of novel rotor endwall contours which have been designed, in part, with the aid of CFD simulations by the research sponsor, Siemens Industrial Turbines Ltd.
Three primary measurement techniques will be used: two non-invasive optical flow visualisation techniques, and one stage efficiency measurement technique
The two optical flow visualisation techniques are Volumetric Velocimetry (V3V) and Carbon Dioxide Planer Laser-Induced florescence (CO2 PLIF). The V3V provides a 3-component velocity field for a volume of fluid; in this case the blade passage. The V3V will be used to visualise the secondary flow features within the rotor blade passage, and gain an understanding of the effect of different endwall contours on these flow features. The CO2 PLIF measurements will provide a visualisation of the egress gas path from the turbine wheelspace. This is important as this gas path effects the formation of secondary flow features in the blade passage.
The stage efficiency measurement technique is a 5-hole pressure probe which is used to determine flow velocity upstream and downstream of the stage. This is used in combination with temperature and rotor toque measurements to calculate stage efficiency, which is of primary importance to the engine designer.
This research will determine the effectiveness of different endwall contours on increasing stage efficiency when compared to the baseline endwall contour that has been used historically in gas turbine design. It will also allow for a greater understanding of the fundamental cause and effect with regards to individual aspects of endwall contour features, e.g. troughs and peaks, and the resulting changes in the secondary flow structure. This knowledge will potentially have a lasting impact on the design procedure of endwalls in industrial gas turbines.