Aero-Thermal Aspects of Endwall Cooling Flows in a Gas Turbine Nozzle Guide Vane

Abstract

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.