Optimisation of the internal cooling duct of a modern turbine blade, consisting of ribbed and pin finned sections, is essential as the coolant flow introduces losses that need to be minimised. In the ribbed sections large variations in turbulence levels occur and the secondary flows associated with these ribs are responsible for significant local heat transfer variations. This paper presents a finite difference simulation of the friction losses and heat transfer rates in a typical duct with two passes. A standard k-ε turbulence model with wall functions is used as a turbulence closure model. The results show predicted heat transfer enhancement in a typical two pass duct for both smooth walls and a duct with ribs on the top and bottom surfaces. In the case of a smooth duct, predicted and measured results were in good agreement in areas where no recirculation occurred. At the ribbed walls, and in the areas where recirculation occurs, the simulations presented poor results. From the results can be concluded that a wall function based turbulence model does not provide sufficiently accurate results when applied to ribbed ducts and in particular sharp turns.

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