DOUBLE-JET FILM-COOLING FOR HIGHLY EFFICIENT FILM-COOLING WITH LOW BLOWING RATIOS

摘要

Further improvement of the thermal efficiency of modern gas turbines can be achieved by a further reduction of the cooling air amount. Therefore, it is necessary to increase the cooling effectiveness so that the available cooling air fulfils the cooling task even if the amount has been reduced. In particular, the cooling effort for the vanes and blades of the first stage in a modern gas turbine is very high. The task of the film-cooling is to protect the blade material from the hot gas attack to the surface. Unfortunately, aerodynamic mixing processes are enhanced by secondary vortices in the cooling jets and, thus, the film-cooling effectiveness is reduced shortly behind the cooling air ejection through the holes. By improvement of the hole positioning the negative interaction effects can be reduced. The Double-jet Film-cooling (DJFC) Technology invented by the authors is one method to reach a significant increase in film-cooling effectiveness by establishing an anti-kidney vortex pair in a combined jet from the two jets starting from cylindrical ejection holes. This has been shown by numerical investigations and application to an industrial gas turbine as reported in recent publications. Whereas the original design application has been for moderate and high blowing ratios, the present numerical investigation shows that the DJFC is also applicable for lower blowing ratios (0.5 30 hole diameters).