Browsing by Author "Alqefl, Mahmood"

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    Aero-Thermal Aspects of Endwall Cooling Flows in a Gas Turbine Nozzle Guide Vane
    (2019-01) Alqefl, Mahmood
    Gas 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.
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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.