Film Cooling From a Single Row of Cylindrical Angled Holes With Triangular Tabs Having Different Orientations

Abstract

The effect of discrete delta (or triangular)-shaped tabs with different orientations on the film cooling performance from a row of cylindrical holes is investigated. The holes are inclined at 35° along the streamwise direction and the tabs are located along the upstream edge of the holes. Three tab orientations are investigated: (1) tabs placed parallel to the film cooled surface covering a part of the hole; (2) tabs oriented downward at –45 degrees; and (3) tabs oriented upwards at 45 degrees. Measurements were carried out in a low-speed wind tunnel using the transient liquid crystal technique. The mainstream velocity and free-stream turbulence intensity in the low speed wind tunnel are 9 m/s and 7% respectively and the mainstream Reynolds number based on hole diameter is around 7,100. Three blowing ratios of 0.56, 1.13, and 1.7 are tested. Results show that the tabs oriented horizontally and those oriented downward provides the highest film effectiveness at blowing ratios of 0.56 and 1.13. At blowing ratio of 1.7, the horizontal tabs have the highest effectiveness. The higher effectiveness (200-300%) and higher heat transfer coefficient (25-30%) with the tabs are caused due to the generation of secondary eddies counter-rotating with respect to the kidney pair; these eddies reduce jet penetration and thus increase film cooling effectiveness.