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978-3-8439-2674-4, Reihe Thermodynamik
Endwall Contouring Using Numerical Optimization in Combination with the Ice Formation Method
189 Seiten, Dissertation Universität Stuttgart (2016), Softcover, A5
The high turbine inlet temperatures used in modern gas turbines yield a high thermal loading of the turbines' vane endwalls. This loading can be reduced by the application of contoured vane endwalls, which influence flow and heat transfer close to the endwall in a favorable way and thus reduce the heat load.
The present work deals with the creation of such contours in order to reduce endwall heat transfer. Thereby, two methods were used: the Ice Formation Method (IFM) and numerical optimization. For the IFM, experimental ice layers from another study were used as endwall contours in numerical simulations. In the numerical optimizations, a genetic algorithm in combination with CFD simulations was employed to generate endwall contours with reduced heat transfer.
Within the scope of this thesis, different heat transfer optimized endwall contours were created and compared to the flat endwall baseline. First, heat transfer and the underlying flow features at the endwall were carefully analyzed for the flat baseline. Next, nine ice-contoured endwalls were created from experimental ice layers and compared to the baseline, which showed a global reduction of average heat transfer for all contours. For one contour, the changes in heat transfer and the flow field were outlined in detail. Furthermore, entropy production rates were determined for these contours and compared to the baseline. This proved that the IFM causes a reduction of entropy production. The ice-contoured endwalls were also used as starting geometries for a subsequent numerical optimization. The latter yielded contours which further reduced global heat transfer.
To reduce heat transfer especially in the vane passage, another ice-contoured endwall with enlarged cooling length was examined, but the contour could not achieve the desired heat transfer reduction. In contrast, numerical optimizations with a parametrization based on the flat endwall yielded endwall contours with a significant reduction of heat transfer in the vane passage.
Finally, heat transfer characteristics for the created endwall contours were analyzed for the design Reynolds number of Re=200,000. For the ice-contoured endwalls heat transfer reductions were even higher at this Reynolds number, while the numerically optimized contours featured approximately the same reductions in heat transfer as for the Reynolds numbers at which they were created.