Thermal Management of a Transonic Turbine: Leakage Flow and Endwall Contouring Effects

Abstract

Comparison of heat transfer performance of a nonaxisymmetric contoured endwall to a planar baseline endwall in the presence of leakage flow through a stator-rotor rim seal interface is reported in this paper. Heat transfer experiments were performed on a high turning turbine airfoil passage at a transonic exit Mach number at different leakages to mainstream mass flow ratios. The contoured endwall geometry was optimized for secondary flow aerodynamic losses. Transient infrared thermography was used to measure the endwall surface temperature. Simultaneous calculation of the heat transfer coefficient (HTC) and adiabatic cooling effectiveness (ETA) was performed assuming one-dimensional semi-infinite transient conduction. Results show nominal reduction in the area-averaged HTC but significantly higher coolant film coverage using the contoured endwall compared to baseline endwall at different levels of coolant MFR. Interestingly, significant reduction in the area-averaged heat transfer coefficient was observed for cases without coolant flow in the presence of a purge slot when compared with a solid cascade without any cooling features. The backward-facing step seemed to have a first-order impact on endwall heat transfer coefficient distribution compared to coolant blowing cases. The contoured endwall also showed major improvement in net heat flux reduction (combining the effects of the HTC and ETA) especially near the suction side of the platform.