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Computational Method
Within the frame of the presented computations a commercial CFD systems has been employed. FINE/Turbo, developed by NUMECA Int. S. A (NU – MECA (2002)), is a specialized CFD package for all sort of turbomachinery applications. The package includes grid generation, the flow solver and a post processing software. All program modules are embedded into a turbomachinery specific environment.
The numerical scheme solves the 3D Reynolds-averaged Navier-Stokes equations (RANS) on general structured non-orthogonal multi-block grids. The flexibility of the structured grids is greatly enhanced by use of so-called "Full Non Matching Connections", a technique, which allows to arbitrarily connect grids block of different grid topologies or point numbers to each other.
The numerical algorithm incorporated into FINE/Turbo is an explicit four stage Runge-Kutta scheme (Jameson and Baker (1984)). A variety of convergence acceleration techniques are employed, such as implicit residual smoothing, dual time stepping and full multigrid. Space integration is performed us-
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Table 1. Design Data of the MT-1 Turbine
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ing a second order cell-centered finite volume discretization with second and fourth order artificial dissipation. Coarse grid calculations can be carried out in an automatic way on every coarser grid level.
A number of turbulence models are available within FINE/Turbo. In the scope of the present work the algebraic turbulence model of Baldwin and Lomax (1978) has been chosen. All solid walls have been treated as fully turbulent. The authors are well aware that a simple turbulence model and the assumption of fully turbulent boundary layers cannot capture sufficiently accurate the quite complex turbulent structures typical for film cooling. With the main objectives of this study in mind, comparing a fully discretized film cooling geometry with a source term approach, the use of a somewhat simpler model seemed justified and effective. Moreover, new experimental data suggest (Ardey (1998)) that in film cooling simulations the use of any eddy viscosity turbulence model is questionable due to the extreme anisotropic nature of turbulence in these cases.
