Double-Jet Ejection of Cooling Air for Improved Film Cooling

Film cooling in gas turbines leads to aerodynamic mixing losses and reduced temperatures of the gas flow. Improvements of the gas turbine thermal efficiency can be achieved by reducing the cooling fluid amount and by establishing a more equal distribution of the cooling fluid along the surface. It is well known that vortex systems in the cooling jets are the origin of reduced film-cooling effectiveness. For the streamwise ejection case, kidney vortices result in a liftoff of the cooling jets; for the lateral ejection case, usually only one dominating vortex remains, leading to hot gas flow underneath the jet from one side. Based on the results of numerical analyses, a new cooling technology has been introduced by the authors, which reaches high film-cooling effectiveness as a result of a well-designed cooling hole arrangement for interaction of two neighboring cooling jets (double-jet film cooling (DJFC)). The results show that configurations exist, where an improved film-cooling effectiveness can be reached because an anti-kidney vortex pair is established in the double-jet. The paper aims at the following major contributions: (1) to introduce the DJFC as an alternative film-cooling technology to conventional film-cooling design; (2) to explain the major phenomena, which leads to the improvement of the film-cooling effectiveness by application of the DJFC; and (3) to prove basic applicability of the DJFC to a realistic blade cooling configuration and present the first test results under machine operating conditions.