Effect of Upstream Purge Slot on a Transonic Turbine Blade Passage: Part 2 — Heat Transfer Performance

Heat transfer experiments with and without upstream purge cooling were carried out for a high turning (127°) airfoil passage in the presence of an upstream purge slot in a transonic linear cascade. Different coolant to mainstream mass flow ratios (MFR) were investigated at cascade design exit Mach number (0.88) and design incidence angle. The experiments were performed at Virginia Tech’s transient transonic blow down facility. A transient Infrared thermography technique was employed to measure the endwall surface temperature. Heat transfer coefficient (HTC) and film cooling effectiveness (ETA) were calculated from measured temperature assuming a 1-D semi-infinite transient conduction through a solid with convective boundary condition. In this experiment, the blade span increases in the mainstream flow direction in order to match realistic inlet/exit airfoil surface Mach number distribution. Results indicate strong interactions between coolant flow and cross passage secondary flow where significant coolant coverage is observed at higher leakage flow rates through the purge slot. The backward facing step created by the purge slot seems to be the driving factor on influencing endwall HTC compared to with or without blowing cases. Three-dimensional viscous CFD has also been performed for further insight of flow characteristics and to support experimental data. Aerodynamic measurements at cascade exit plane are provided in the companion paper GT2013-94951 [1], “Effect of upstream purge slot on a transonic turbine blade passage: Part – 1 – Aerodynamic performance”.