Influence of Compressibility on Film-Cooling Performance

摘要

Film-cooling is an active cooling technique that is widely used in conventional gas turbine and rocket engines tonmanage heat transfer between hot reacting gases and cooler structural components. It is also a candidate technologynfor the thermal protection of scramjet engines, in which combustion occurs under highly compressible conditions.nThis paper extends semi-empirical modeling ideas for incompressible wall-jet slot film-cooling to account for bothnconvective and thermal compressibility effects. The new model shows that the influence of compressibility isndetermined by themagnitude of the average convectiveMach numberMc, the total temperature ratio u00010 u0001 T0s=T01,nand the flow Mach number MHS of the highest-speed stream in the film-cooling flow. In general, increasing Mc andndecreasing u00010 improves film-cooling performance.These predictions are validated via comparisonwith experimentalndata in three compressible flow regimes: weakly compressible (Mc, MHS u0002 0:3 and 0:6 u0002 u00010 u0002 1), moderatelyncompressible (0:3 1:0, and u00010 < 0:3).nThe model also resolves disagreements in the literature over the importance of compressibility in film-coolingnproblems by showing that compressibility effects can be significant, provided the convective and flowMach numbersnare high enough and the total temperature ratio is low enough.