Film-cooling has become a widely used cooling method in present day gas turbines. Cooling gas ejection at the leading edge serves to protect the entire vane surface from contact with the hot gas. Thus, material temperatures must be reduced in order to guarantee an economically acceptable life span of the vane.
Normally, thermal investigations are performed with frozen equilibrium temperature distributions for different operating points. Thus, the heat transfer interaction between the flow and the solid body is neglected. This influence is taken into account by a conjugate fluid flow and heat transfer method in the investigations to be presented. In the case of the aerodynamics, a solver for the 3-D full Navier-Stokes equations is employed. The numerical scheme works on the basis of an implicit finite volume method combined with a multi-block technique.
In the 3-D numerical experiment to be presented, the influence of leading edge cooling gas ejection on the temperature distribution to the vane material is investigated. The cooling air is ejected through two slots at the leading edge. 3-D aerodynamic investigations performed by Bohn et al. (1996a) have shown the influence of complex 3-D flow phenomena, e.g. secondary flow, on the distribution of the cooling air along the vane surface. Furthermore, 3-D thermal investigations for one operation point with a realistic temperature ratio of cooling air flow and main flow were presented by Bohn et al. (1996b).
The investigations were performed for three different flow angles in the non-ejection case and the film-cooled case in order to demonstrate the operation of the cooling method. The shift of the stagnation line significantly influences the cooling fluid distribution along the vane surface, something that has consequences for the thermal load of the vane. Furthermore, the results are compared to an investigation with a prescribed frozen equilibrium temperature distribution. It is shown that the vane temperature increases locally for over 10 K at different operating points. This increase is significant for the thermal design process and can only be detected using the conjugate fluid flow and heat transfer method.