AN EXPERIMENTAL INVESTIGATION OF SHOWERHEAD FILM COOLING PERFORMANCE IN A TRANSONIC VANE CASCADE AT LOW AND HIGH FREESTREAM TURBULENCE

This experiment investigates the effects of blowing ratio on the film cooling performance of a showerhead-cooled first-stage turbine vane at low freestream turbulence (Tu = 2%) and an integral length scale normalized by vane pitch (Lambda(x)/P) of 0.05. The exit Reynolds number based on vane true chord is 1.1 x 10(6). The effect of freestream turbulence at high Mach number (M-ex = 0.76) and blowing ratio (BR = 0, 1.5, 2.0) is also explored by comparing results with high freestream turbulence measurements (Tu = 16%) previously performed in the same cascade. To characterize film cooling performance, platinum thin-film gauges were used to measure Nusselt number and film cooling effectiveness distributions at the midspan of the vane. Net heat flux reduction is also addressed. The primary effects of coolant injection were augmentation of Nusselt number and reduction of adiabatic wall temperature on the vane surface. In general, increasing blowing ratio showed increases in Nusselt number augmentation over the vane surface and an increase in film cooling effectiveness as well. Both Nusselt number and film cooling effectiveness trends were influenced by a strong favorable pressure gradient and resulting flow acceleration on the suction surface. Comparing low freestream turbulence results with high freestream turbulence measurements showed that large-scale, high freestream turbulence can decrease heat transfer coefficient and film cooling effectiveness downstream of injection.