Convective Heat Transfer to Gas Turbine Blade Surfaces

Abstract

Results are given of experiments into the variation, with chordwise position, of the heat transfer between the surface of a typical gas-turbine blade in cascade and in the air stream. The principal variables investigated are the blade's Reynolds number and the incident angle of the air stream, while the air/temperature ratio of the blade is kept near unity. It is shown that, with certain provisions, the results should be broadly applicable to similar blades under normal operating conditions. The extent of the correlation of the results with values obtained by available theoretical methods is shown. The laminar boundary-layer heat-transfer theory due to Squire (1942)‡ gives good agreement, but the predictions of heat transfer in the regions of turbulent boundary-layer flow, particularly under negative pressure gradients, leave much to be desired. In addition, knowledge of conditions at transition to turbulence and at laminar separation of the boundary layer is scanty, with consequent uncertainty in any overall heat-transfer forecast. Minor suggestions in this respect have resulted in slightly improved correlations. The experimental method employed involved the manufacture of a wind tunnel having a form of contraction based on the theoretical work of Cheers (1945), which gave excellent results; also a novel process was developed for the manufacture of the cascade blade which, it is considered, possesses certain advantages over the more traditional methods.