Browsing by Subject "Secondary Flows"
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Item Aero-Thermal Aspects of Endwall Cooling Flows in a Gas Turbine Nozzle Guide Vane(2019-01) Alqefl, MahmoodGas turbine engines are still one of the favorite sources for shaft power. They are relatively clean and higher in efficiency than other common sources, and their working principle makes them especially practical for aircraft propulsion. Over the past decades, the desire for higher turbine inlet temperature has increased to achieve higher specific power and efficiency. Currently, the temperature of the gasses entering the turbine is typically higher than the melting point of its components. This leads to the need of effective turbine cooling. Endwalls are particularly challenging to cool due to the complex system of secondary flows near its surface that washes the protective film coolant into the mainstream. This three-dimensional aerodynamics is also a source for irreversibility. Due to the nature of film coolant injection, its interaction with endwall aerodynamics is coupled. The film coolant momentum affects the secondary flow formation, and the secondary flows affect the film coolant distribution over the endwall. To achieve better endwall designs and cooling schemes, better understanding of this interaction is needed. This thesis studies experimentally the aero-thermal interaction of cooling flows near the endwall of a first stage nozzle guide vane passage. The test section involves engine representative combustor-turbine interface geometry, combustor coolant, and endwall film cooling flows injected upstream of a linear cascade. The approach flow conditions represent flow exiting a low NOx combustor. The aero-thermal interaction is studied through detailed measurements of passage velocity fields, thermal fields and endwall adiabatic effectiveness for various film cooling mass flow to mainstream flow ratio (MFR). The contribution of combustor coolant towards cooling the endwall is also presented. The detailed measurements revealed a new dominant vortex in the passage that is opposing the passage vortex. This vortex dominates the coolant mixing and migration and completely changes our understanding of the system of secondary flows present in a film cooled nozzle guide vane passage.Item Secondary Flow, Turbulence, and Film Cooling Measurements in a Gas Turbine Vane Passage Downstream of a Novel Combustor-turbine Interface(2022-04) Nawathe, KedarGas turbines are essential in electrical power generation and aircraft applications. One way to increase the efficiency of a gas turbine engine is to increase the combustor exit temperature. However, temperatures higher than the melting point of turbines located downstream can result in serious thermal failures. Therefore, these high temperatures create a need to design aggressive cooling schemes for engine sections to prevent component damage. However, owing to the complexity of the flow in the engine, it is essential to understand how coolant flows interact with engine passage flow. This thesis discusses three experimental studies relating to the cooling of gas turbines:(1) Evolution of secondary flows: Due to the geometry of turbine vanes, various undesired flows are developed in the vane passage, which are termed as secondary flows. The flowrates of the injected coolants affect the way in which these secondary flows are generated and transported. A detailed description of the vane passage secondary flowfield for a variety of coolant flowrates is provided and discussed. (2) Film cooling performance: The injected coolant forms a film on the surfaces to be cooled to protect them from failure. The cooling performance of a novel coolant injection scheme is reported in this study. Coolant transport is recorded using temperature and velocity measurements. The cooling performance on the vane passage surfaces is discussed using these transport measurements and compared with injection scheme currently used in the engine. (3) Decay of turbulence: Vane geometry leads to changes in turbulence features of the flow, which are known to affect the cooling of the vane surfaces. Such changes to turbulence were measured and discussed. Numerical simulations using Reynolds-averaged Navier-Stokes turbulence models were also performed for the same vane geometry. A comparison between the computed and the measured parameters is also presented. The results of these studies are meant to help gas turbine designers in reducing the amount of required coolant which would lead to an increase in the gas turbine efficiency.