An extensive numerical study was accomplished in order to accompany an experimental research program. The present work is focussed on the influence of the shape and the inclination of film cooling holes on the aerodynamic of the turbine cooling flow. Four different cooling hole geometries located on the suction side of a large scale turbine cascade were modelled and numerically simulated over the entire range of practically applicable blowing ratios. The thermodynamic conditions chosen, were in order to simulate comparable engine conditions.
Having computer limitations in mind, former simulations had to cope with either of two limitations. Meshing the entire domain led to an insufficient grid resolution in the vicinity of the ejection area, omitting valuable detailed flow information. In contrast, the so-called local approach (Vogel, 1996) overcame this problem by isolating an area close to the ejection zone, hence leading to a proper numerical resolution. A major drawback of this method is the required assumption for a limiting streamsurface, which often led to an inaccurate pressure distribution on the blade surface. Therefore, a new numerical technique in applying a 3D Navier-Stokes code on cooling flow problems — the global approach — was used, overcoming the restrictions of the above mentioned approaches. In the frame of these numerical investigations the commercially available CFD-package FINE™/Turbo by NUMECA was used.
The CFD-package incorporates a modern flow solver and the capability to perform multi-species computations, which was utilised herein. A second species (tracer gas) with the properties of air, was introduced, ejecting from the cooling plenum, hence strongly facilitating the visual detection of the emerging and dispersing cooling flow. The numerical resolution reached well over one million grid points.
The distributions of the tracer concentration and the oil and dye visualisations clearly reveal a strong dependency between the cooling hole shape and the efficiency of the film cooling. A considerable increase in the latter could be achieved, if non-cylindrical cooling hole geometries were used. The CFD simulations are in a very good agreement with the measurements (Ganzert, Hildebrandt and Fottner, 2000), clearly uncoveringvery detailed flow phenomena, which could also be detected in the experimental results. It was found out that the shape and the inclination angle of the cooling holes are of paramount importance to the distributing pattern of the cooling air and hence to the cooling efficiency.
A Numerical Study On Active Film Cooling Flow Control Through The Use Of Sister Holes
