Heat Transfer in 3D-Vane-Passages - Systematic Generation and Investigation of Contoured Vane-Endwall Geometries for Turbomachines Using the Ice Formation Method

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The research project Wärmeübergang in 3D-Schaufelkanälen, has been designed for 4 years. The present proposal is now for the second phase (3rd and 4th year) of the project. In the first 2 years, the ice formation method was successfully used for the creation of novel vane-endwall configurations considering the heat transfer reduction on the vane endwall. Endwall configurations could be found, that show reduced integral heat transfer up to 11% compared to an uncontoured endwall. Investigations in the second phase of the project will depict further potential for improvement. Aspects of the transient ice growth will be investigated in more detail. It will be clarified, whether during the growth of the ice layer other interesting topologies will already be formed, which feature local optima in pressure loss and/or heat transfer behavior. For that purpose, contours at multiple points in time prior to the steady state will experimentally be investigated and analyzed in terms of entropy production rates, heat transfer, and pressure loss. In order to determine how different initial conditions in the optimization process affect its results, numerical optimizations will be conducted with these ice contours as initial geometries. Since it has become apparent that also the regions in front of and behind the cascade considerably influence the heat transfer at the endwall, the cooled area will be extended to these regions. Thereby, more degrees of freedom are provided and topologies are developed, that are optimized not only in the region between the vanes but also in the transition regions to the up- and downstream components. The experimentally generated ice contours will be used as initial geometries for numerical optimizations with multiple goal functions and the resulting contours will be analyzed. An expansion of the numerical investigations to gas turbine specific conditions shall guarantee that resulting contours are not only of academic interest but will also be useful for real applications.Furthermore, endwall contouring with additional injection of cooling fluid through a slot in front of the vanes will be investigated in order to see what kind of influence the injection has on the ice topology and what kind of contours develop, when these topologies are used as initial geometries for the numerical optimization process. By the use of a concluding inspection of all endwall contours generated in this project, improved topology elements for endwall contouring shall be identified and recommendations for the contouring of endwalls will be given. These recommendations allow to generate future endwall contours, which are better adapted to the respective application. For example, the use of an endwall contour for minimum heat transfer reduces the required cooling air noticeably and therefore leads to enhanced life time of the components and to a higher thermal efficiency of the turbine.