Experimental investigation of film cooling effectiveness for slots of various exit geometries

Abstract

A parametric study was conducted to experimentally determine the effects slot exit geometries have on film effectiveness (ijy) for several injection angles (a = 0.0, 5.0, 8.5, 11.5, and 15.0 deg). Such slot geometries are typically used on the pressure side trailing edge of jet engine turbine airfoils, providing cooling film to protect the trailing edge, which is often a life limiting area. Four different slot lip thickness to height ratios (tls = 0.5, 0.75, 1.0, and 1.25) and three different slot width to height ratios (w/s = 2, 5, and 17) were tested over a blowing ratio (M = (pU)c/(pU)h) range of 0 to 1.3. All geometries were tested at a constant density ratio (pc/ph) of 1.4. Slot surface film effectiveness measurements were made over a range of downstream surface distance to slot height ratios (x/s) of 0 to 15. Five different density ratios (pclph = 1.2, 1.3, 1.4, 1.5, and 1.6), spanning the typical engine operating range, were tested for one geometry to determine the effect of density ratio on film effectiveness. Correlations are shown for film effectiveness (rjf) in terms of the nondimensionalized downstream distance (x/Ms). The results show that: a) ij/is highly sensitive to tls, but not significantly sensitive to either w/s or pclph and b) an optimum injection angle equal to 8.5 deg exists for xlMs values less than 60.