Influence of Mainstream Turbulence on Leading Edge Film Cooling Heat Transfer Through Two Rows of Inclined Film Slots

Abstract

The effect of film slot injection on leading edge heat transfer coefficient and film cooling effectiveness under high mainstream turbulence conditions was experimentally studied for flow across a blunt body with a semicylinder leading edge and a flat afterbody. High mainstream turbulence levels were generated by a bar grid (Tu = 5.07 percent) and a passive grid (Tu = 9.67 percent). The incident mainstream Reynolds number based on the cylinder diameter was about 100,000. The spanwise and streamwise distributions of the heat transfer coefficient and film effectiveness in the leading edge and on the flat sidewall were obtained for three blowing ratios (B = 0.4, 0.8, and 1.2) with two rows of film slots located at ± 15 and ± 40 deg from the stagnation line. The cross-sectional slot length-to-width ratio was two. The slots in each row were spaced three cross-sectional slot lengths apart and were angled 30 and 90 deg to the surface in the spanwise and streamwise directions, respectively. The results show that heat transfer coefficient increases with increasing blowing ratio, but the film effectiveness reaches a maximum at an intermediate blowing ratio of B = 0.8 for both low (Tu = 0.75 percent) and high (Tu = 9.67 percent) mainstream turbulence conditions. The leading edge heat transfer coefficient increases and the film effectiveness decreases with mainstream turbulence level for the low blowing ratio; however, the mainstream turbulence effect decreases for the high blowing ratio. The leading edge heat load is significantly reduced with two rows of film slot injection. The blowing ratio of B = 0.4 provides the lowest heat load In the leading edge region for the low mainstream turbulence, but B = 0.8 gives the lowest heat load for the high mainstream turbulence conditions.