Browsing by Subject "Turbomachinery"

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    An Experimental and Numerical Investigation of Endwall Aerodynamics and Heat Transfer in a Gas Turbine Nozzle Guide Vane with Slot Film Cooling
    (2016-12) Alqefl, Mahmood
    In many regions of the high-pressure gas turbine, film cooling flows are used to protect the turbine components from the combustor exit hot gases. Endwalls are challenging to cool because of the complex system of secondary flows that disturb surface film coolant coverage. The secondary flow vortices wash the film coolant from the surface into the mainstream significantly decreasing cooling effectiveness. In addition to being effected by secondary flow structures, film cooling flow can also affect these structures by virtue of their momentum exchange. In addition, many studies in the literature have shown that endwall contouring affects the strength of passage secondary flows. Therefore, to develop better endwall cooling schemes, a good understanding of passage aerodynamics and heat transfer as affected by interactions of film cooling flows with secondary flows is required. This experimental and computational study presents results from a linear, stationary, two-passage cascade representing the first stage nozzle guide vane of a high-pressure gas turbine with an axisymmetrically contoured endwall. The sources of film cooling flows are upstream combustor liner coolant and endwall slot film coolant injected immediately upstream of the cascade passage inlet. The operating conditions simulate combustor exit flow features, with a high Reynolds number of 390,000 and approach flow turbulence intensity of 11% with an integral length scale of 21% of the chord length. Measurements are performed with varying slot film cooling mass flow to mainstream flow rate ratios (MFR). Aerodynamic effects are documented with five-hole probe measurements at the exit plane. Heat transfer is documented through recovery temperature measurements with a thermocouple. General secondary flow features are observed. Total pressure loss measurements show that varying the slot film cooling MFR has some effects on passage loss. Velocity vectors and vorticity distributions show a very thin, yet intense, cross-pitch flow on the contoured endwall side. Endwall adiabatic effectiveness values and coolant distribution thermal fields show minimal effects of varying slot film coolant MFR. This suggests the dominant effects of combustor liner coolant. show dominant effects of combustor liner coolant on cooling the endwall. A coolant vorticity correlation presenting the advective mixing of the coolant due to secondary flow vorticity at the exit plane is also discussed.
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    Experiments on Film Cooling of Gas Turbine Vane Passage Surfaces: The Effects of Various Distributions of Combustor Coolant and Endwall Injection Coolant
    (2019-08) Nawathe, Kedar Prasad
    The efficiency of gas turbines is known to increase with the exit temperature of the combustor gases. However, this temperature is limited by the melting point of various equipment downstream of the combustor. To increase this limit, coolants injected at different locations form low-temperature films on the surfaces of these regions to avoid melting and thermal stress damage. This injection significantly changes the flow field in the vane passage. Therefore, there is a need to study the aerodynamic and thermal effects of combustor, transition duct and passage coolant injection, which can assist the designers of gas turbines to employ better cooling schemes with minimal use of coolant, thus increasing the efficiency and durability of turbines. The study presented in this thesis discusses experimental tests performed to understand the coolant effectiveness for cooling the endwall and vane surfaces of a nozzle guide vane cascade. The test section contains an engine representative combustor-turbine interface along with a contoured endwall. High turbulence intensity as well as high Reynolds numbers are achieved in the facility to closely simulate engine conditions. In addition to recording the surface effectiveness values, in-field thermal and aerodynamic measurements were taken. It has been previously discovered that the effusion and louver coolants, used to cool the combustor section, can also be credited in cooling the endwall and the vane surfaces. Therefore, this study is helpful to understand the effects of changing the mass flow ratios of different coolants injected upstream of the passage. Especially, louver coolant injection in the combustor transition duct region, due to its location and injection angle, is suspected to provide significant passage endwall cooling. In-field measurements provide insight to the coolant transport through the passage and its interaction with the mainstream. As the net combustor coolant momentum is higher than the film coolant momentum, the changes in the flow field due to its injection are more significant and are sustained to the end of the passage, giving more streamwise coverage than with a conventional film cooling setup. The film coolant mass flow ratio is varied in this study to see how the interaction of different coolants changes with changes of their injected momentum. The measurements reveal that the upstream coolant flow helps in keeping the film coolant attached to the endwall for most of the passage and also keeping the film thickness fairly uniform in the pitchwise direction. An increase in louver coolant mass flow rate shows higher endwall cooling effectiveness. The velocity contours show that a dominant vortex is present due to combustor coolant injection and that the passage vortex was, although present, diminished due to this other vortex. While changing the louver coolant mass flow rate did not change the intensity of these vortices, changes in the film coolant mass flow rate increased the intensity of the dominant vortex near the pressure surface. Also, the presence of this new vortex helps in film cooling the pressure surface, a region where, conventionally, the least amount of coolant coverage is recorded.
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    Secondary Flow, Turbulence, and Film Cooling Measurements in a Gas Turbine Vane Passage Downstream of a Novel Combustor-turbine Interface
    (2022-04) Nawathe, Kedar
    Gas 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.