Film-cooling has become a widely used cooling method in present day gas turbines. Cooling gas ejection at the leading edge serves to protect the entire vane surface from contact with the hot gas. With doing this, material temperatures are reduced in order to guarantee an economically acceptable life span of the vane.

This paper describes the application of a numerical method for the conjugate calculation of internal and external fluid flows and the heat transfer in and through the blade walls of a film-cooled turbine guide vane. The advantage of this approach is that it is possible to predict fluid flow properties and wall temperatures without the need for additional heat transfer conditions or temperature conditions at the external surfaces of the vane. This is a great advantage because the desired data are either unknown or not available for the calculation in the design process of new cooled blades or vanes. In a complete calculation of external and internal flows, no additional boundary conditions at the internal surfaces of the cooling geometry are needed either. Another advantage is the interaction of fluid flow and heat transfer which is taken into account by the conjugate calculation.

In the 3-D numerical experiment to be presented, the influence of leading edge cooling fluid ejection on the temperature distribution in the vane material is investigated. The cooling fluid is ejected through two slots at the leading edge. The calculations are performed for three blowing ratios in order to investigate the efficiency of the cooling method. Realistic temperature ratios of cooling-fluid flow and main flow are considered. Such information is very useful in the aero thermal design process of new cooling configurations, since the amount of experimental work can be minimized. The results show the influence of complex 3-D flow phenomena (e.g. passage vortex) on the cooling fluid distribution on the vane surface as a function of the chosen blowing factor. Due to the influence of the passage vortex, the cooling fluid is displaced and leaves the vane surface near the side-wall uncovered against the hot gas. Furthermore, cooling fluid displacement on the pressure side according to the ejection slot geometry leads to another unprotected region on the vane surface. These effects have severe consequences on the thermal load of the vane and can reduce its life span.

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