Computations have been carried out to support the understanding and analysis of film cooling measurements on a heavily film cooled HP turbine vane currently performed at EPFL-LTT. The cooling layout comprises cylindrical holes in the leading edge region (showerhead cooling) and shaped holes on suction and pressure side. Adiabatic film cooling effectiveness and heat transfer coefficients were determined by applying the transient liquid crystal measurement technique. The measured results showed non-symmetrical distributions of coolant downstream of the coolant holes which could not be explained by the hole arrangement. Since several references indicate a strong influence of the internal flow on the coolant distribution at the surface of the airfoil, a numerical investigation was performed. The geometry of the tested airfoil being very complex (113 cylindrical and shaped holes), the problem was decomposed in three different computations, realized with FLUENT, in order to obtain the adiabatic film cooling effectiveness in the vicinity of a cooling hole. The first computation determines the outer flow on a smooth airfoil; the second computation comprises the complete internal geometry, ie. the plenum and the cooling holes. Finally the third computation is carried out for an isolated cooling hole with small parts of the plenum and the external flow domain with boundary conditions extracted from the results of the first two computations. The so gained numerical results are in very good agreement with the experimental findings both in qualitative and quantitative aspects. They confirm the important effect of the flow inside the plenum on the film cooling effectiveness at the surface of the airfoil. It can thus be concluded that it is possible to predict the film cooling behavior of complex geometries by decomposing the problem into several cases of lower complexity.
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