The improvement of the thermal efficiency of modern gas turbines can be achieved by reducing the required cooling air amount. The reduction of the cooling air claims for an improved cooling technology, which assures the protection of the vane and blade airfoil from the hot mainstream flow. Consequently, it is required to increase the cooling efficiency of applied cooling technologies. Streamwise ejection from a cylindrical hole causes kidney vortices, which transport hot gas underneath the cooling jet and leads the cooling jet to lift off the surface. The double-jet film cooling technology represents a solution to establish an anti-kidney vortex, which prevents the double jet from lifting off the surface and raises the lateral spreading of the cooling air. This is achieved by a particular arrangement of simple cylindrical holes to each other. Additionally, the design of double-jet holes reduces significantly the effort of hole manufacturing compared to the effort of manufacturing a shaped hole design. Numerical investigations for blowing ratios from M = 0.5 up to M = 2 and experimental investigations in a test rig prove the proper film cooling ability of the double-jet film cooling technology. Furthermore, this paper presents a numerical parametric study of the double jet film cooling technology. The influence of the lateral ejection angle on the distribution of the cooling film is calculated and analyzed for the blowing ratios of M = 1, M = 1.5 and M = 2. It can be shown that an even higher film cooling effectiveness is reached with the use of the double-jet film cooling technology by an improvement of the hole positions and hole angles than in previous investigations.
Film Cooling in Rocket Nozzles