A numerical study has been conducted to investigate the effects of film cooling on turbine capacity in transonic HP NGVs. The study is part of a wider research program the aim of which is to quantify the sensitivity of capacity predictions to the methods of numerical prediction.

Results of two dimensional CFD are presented for the case of single and multiple film cooling rows. The capacity characteristics (with pressure ratio) for modern airfoil profiles, and the change in capacity with film cooling are investigated. The interaction between rows is shown to be weak, and possibility of using superposition techniques is discussed. The effect of turbulence model on the change in capacity with film cooling is discussed.

The CFD simulations are compared to a simple analytical two dimensional mixing model developed to aid fundamental understanding of the problem. The effect of film cooling on turbine capacity is modelled by considering a mainstream flow displaced by a partially mixed film cooling layer. The model uses fundamental cooling performance parameters which can be estimated an early stage of the engine design process, providing a means for early assessment of the correction due to film cooling.

It is argued that it may be unnecessary to simulate film cooling in capacity predictions.

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