Heat Transfer Coefficients and Film Cooling Effectiveness on the Endwall of a Transonic Turbine Vane Measured With the Reference Luminophore of Binary Pressure-Sensitive Paint

Abstract

Film cooling is a key technique used to reduce heat transfer from hot combustion gases to stationary and rotating components in a gas turbine engine. In high-performance engines, the endwall experiences high heat gains due to flattened mainstream temperature profiles and low solidity ratio airfoils. In this study, the thermal performance of upstream film cooling holes on the endwall of a transonic, five-vane, annular sector cascade was characterized. Transonic measurements of the adiabatic film cooling effectiveness are typically performed with the binary pressure-sensitive paint, which has a reference sensor to allow compensation for temperature variation. A novel experimental technique has been demonstrated that extends the measurement capability of the binary pressure-sensitive paint by using the reference sensor to measure the temperature and heat transfer coefficient. These measurements were performed in a transient heat transfer experiment assuming 1D conduction through a semi-infinite solid exposed to a convection boundary. The mainstream exit Mach number was 0.9, and the coolant-to-mainstream density ratio was 1. The coolant-to-mainstream mass flow ratio was varied from 0.75% to 1.25%. An optimum mass flow ratio of 0.75% was identified as it provided the lowest area-averaged heat transfer coefficient while increasing it had little impact on the film cooling effectiveness.