Film Cooling on Turbine Vane Endwalls with Different Inlet Cooling Configurations: Experimental and Computational Results

A comparative study of turbine endwall film cooling resulting from three different cooling configurations in front of the passage inlet was conducted. The three inlet cooling configurations considered in this study were a conventional continuous slot, double rows of discrete film holes, and an interrupted slot with a backward-facing step. Pressure sensitive paint (PSP) was sprayed over the endwall surfaces to map adiabatic cooling effectiveness contours and five-hole probe and thermocouple measurements were implemented to assess aero-thermal fields at the passage exit. The evolution of cooling effectiveness was compared across a full range span of coolant flow rates of 0.3-1.8% in a real engine. Additionally, complex flow structures inside the passage due to interactions of coolant with mainstream flows were visualized using computational fluid dynamics (CFD) simulations to support the observed coolant coverage patterns. A side-by-side comparison of CFD simulations against experiments was made as well to evaluate the reliability of conventional turbulence modeling methods in such a complex flow. The continuous slot was found to produce the highest cooling effectiveness values while the double-row holes offered the most uniform coolant coverage, leading to spreading out of the coolant jets downstream of the passage throat and even beyond the trailing edge of the passage for coolant injection rates higher than 1.0%. Supported by the CFD-predicted flow structures and measured aerodynamic losses, the injection from the double-row holes weakened the passage secondary flows and thus caused the lowest aerodynamic loss. On the contrary, the interrupted slot enhanced the secondary flows due to the backward step, resulting in the highest flow loss.