INVESTIGATIONS ON COOLING HOLE PATTERNS OVER A TURBINE ENDWALL FOR IMPROVING COOLING EFFECTIVENESS

Redistributions of film hole patterns over the endwall region of a turbine vane are investigated in this work, for providing effective coverage for the entire endwall surface. Air enters the linear cascade with a turbulence intensity of 10.8% that is measured in front of the cascade inlet and exits the cascade passage with an averaged Reynolds number of 5.52x10(5). Three film injection patterns are employed: a baseline scheme in which coolant is injected from twelve pressure-side (PS) and four suction-side (SS) discrete holes as well as an upstream slot, a curtain cooling scheme in which two rows of discrete holes (totally thirteen holes) are included in the PS region at the passage inlet, and a hole-redistributed scheme in which the number of the PS holes is reduced and the PS and SS holes are redistributed. Film cooling effectiveness over the endwalls cooled by the three injection patterns is measured using the pressure-sensitive paint (PSP) technique for a density ratio of 1.5 and typical coolant flow rates found in a real engine. Additionally, aerodynamic data is measured by a five-hole probe at the cascade exit to demonstrate the effects of the injection from different hole patterns on flow fields throughout the cascade passage. Comparisons among the three hole patterns reveal that by increasing coolant rates, cooling effectiveness from the slot injection is significantly increased while that from the curtain injection upstream the passage inlet and hole injection within the passage is slightly varied. Although the slot injection is an effective cooling source, it leaves the PS region of the endwall passage uncovered, which can be well alleviated by using the curtain cooing instead of the PS hole injection. Overall, the curtain cooling provides better cooling effectiveness at an equal or even lower coolant flow rate, compared with the baseline configuration, and the hole-redistributed scheme generates better local cooling performance.