Experimental investigation on effect of cross-flow reynolds number on film cooling effectiveness

Film cooling effectiveness and discharge coefficient of cylindrical holes fed by different internal cross-flow channels with varying cross-flow Reynolds numbers Re_c are investigated. Three cross-flow cases—a smooth case and ribbed cases with 135-deg ribs and 45-deg ribs—are studied at three blowing ratios M and two Re_c . Film cooling effectiveness contours are obtained by the transient liquid-crystal measurement technique. For the smooth case and 45-deg case, the asymmetrical vortex is more pronounced with increasing cross-flow direction velocity, resulting in more skewed film coverage at M 0.5 and Re_c 100;000. Helical motion within the film hole for the 45-deg case is more violent. On the contrary, laterally symmetric film-coverage contours are displayed for the 135-deg case, and the film cooling effectiveness at Re_c 100;000 decreases slowly as flowing downstream. The influence of Re_c on lateral distribution is greater at M 1.0. The lateral spread of film coverage at Re_c 100;000 is wider than that at Re_c 50;000. At M 2.0, there is almost no film coverage in the downstream region at Re_c 50;000. The jet is relatively attached greater to the surface, thus producing positive influence on the film cooling effectiveness at Re_c 100;000. The holeexit velocity contour on the −Y side mainly affects film coverage. The discharge coefficient increases as M increases. The 45-deg case is the lowest, whereas the 135-deg case is the highest.