The present work deals with the development and validation of a method for the automatic aerodynamic optimisation of turbine cascade blades for high pressure stages of heavy duty gas turbines. This class of profiles features aerodynamic and geometric properties which can strongly depart from typical conditions of turbine profiles for aero engines applications. In fact, the Reynolds number and the trailing edge thickness of these profiles can be an order of magnitude higher than the corresponding values of aeronautical gas turbines. In order to gain better insight into these major differences, extensive experimental investigations were performed at the High Speed Cascade Wind Tunnel of the University of the German Armed Forces Munich on various turbine cascade blades designed by ALSTOM. These reference profiles feature characteristics typical for high pressure turbine blades for heavy duty gas turbines. The experimental results furnish an exhaustive database for the validation of the flow solver applied within the developed design method. Furthermore, a comparison of the optimisation results and the reference turbine cascades attests the high potential of the newly developed procedure for the aerodynamic design of highly loaded turbine cascade blades. The developed tool is conceived for the application in an industrial framework and design time scales compatible with industrial requirements have to be considered as well. In this context a method consisting of a two-dimensional RANS flow simulation approach combined with a parametric geometry generator and an optimisation algorithm is proposed. For the simulation of the turbine cascade flow a quasi three dimensional version of the Navier-Stokes solver TRACE from the DLR in Cologne is applied. The parametrical representation of the turbine profiles is realised using the blade geometry generator PROGEN, which is a tool applied successfully for industrial blade design today. Various stochastic global optimisation techniques were tested. The Adaptive Simulated Annealing algorithm demonstrated best properties for a detailed investigation of wide parameter ranges in reduced timeframes. Furthermore, this optimisation algorithm showed best capabilities in handling highly non-linear objective functions, like the scalar objective function used within the present investigations. The main optimisation target in this work was the reduction of the cascade total pressure losses by imposing a fixed operating point. Additional requirements on the profile pressure distribution were introduced as well in order to allow optimal conditions for an efficient cooling of the blade. This is a fundamental aspect for the generation of optimal blade profiles which are of relevance for practical applications. In fact, a major goal of the present work was AbstractXI the development of an erodynamic design method which does not merely optimise the location of the transition zone on the blade suction surface, but also ensures profile velocity distributions satisfying major aerodynamic Requirements for the optimal cooling of the blade (e.g. smooth acceleration on the suction and pressure surface). All these requirements were integrated in a single value objective function. The form of the various components of the scalar function was tailored ad hoc in extensive preliminary studies. Furthermore, some major mechanic and geometric constraints were specified in order to restrict the search to a sub set of realistic geometries. In this way the optimisation task was reduced to a single-objective, constrained approach. The results of the proposed numerical design system indicate that the present method is able to generate automatically blade geometries with reduced losses and featuring profile velocity distributions which ensure favourable conditions for the cooling of the blade. The reliability of the method at changed geometric and mechanical boundary conditions was demonstrated as well. In fact this is an aspect of major importance considering that the aerodynamic design method has to be integrated into a more complex design process where various disciplines with contrasting aims interact and modifications to the basic mechanical and geometrical blade constraints often occur during an iterative blade design process. Die Erhöhung der Turbineneintrittstemperatur ist ein wesentliches Mittel zur Wirkungsgradsteigerung der Gasturbinen. Dies kann nur durch die Anwendung fortschrittlicher Materialien und Fertigungstechniken erzielt werden. Trotz der niedrigeren Temperaturen in Kraftwerks-Gasturbinen im Vergleich zu Flugtriebwerken, sind die Lebenserwartungen für die Komponenten von Gasturbinen für Stromerzeugung deutlicher höher als die für die Komponenten von Flugtriebwerken. All dies erhöht die Kosten für die Herstellung der vorderen Stufen moderner Gasturbinen für stationäre Anwendungen. In diesem Zusammenhang stellt die Reduzierung der Schaufelanzahl einen praktikablen Weg für die Kostensenkung dar. Um die damit verbundene Erhöhung der Belastung bei gleichbleibendem Wirkungsgrad zu ermöglichen, sind neue Auslegungskriterien für diese Klasse von Schaufelprofilen notwendig. Umfangreiche experimentelle Untersuchungen wurden am Hochgeschwindigkeits-Gitterwindkanal der Universität der Bundeswehr München durchgeführt, um Erfahrungen auf typische Schaufelprofile für die Anwendung in stationärer Gasturbinen zu gewinnen. Die experimentellen Daten dienten zur Validierung vorhandener Korrelationen und Rechenverfahren für diesen Einsatzbereich. Darüberhinaus ein automatisches System für die aerodynamische Optimierung zwei-dimensionaler Schaufelgitter wurde entwickelt und auf Basis der vorhandenen experimentellen Daten validiert. Die Methode setzt sich aus einem parametrischen Geometriegenerator, einem Navier-Stokes-Rechenverfahren und einem Optimierungsalgorithmus zusammen. Ziel der Optimierung ist die Reduzierung der Totaldruckverluste bei gleichbleibender Enthalpieumsetzung unter Berücksichtigung der Anforderung an die Machzahl-Verteilung für eine effiziente Kühlung des Profils. Zusätzliche mechanische und geometrische Randbedingungen für die resultierenden Schaufelprofile wurden berücksichtigt. Das entwickelte Verfahren zeigt hohes Potential für die Auslegung hochbelasteter, verlustarmer Turbinenschaufelprofile.    «

The present work deals with the development and validation of a method for the automatic aerodynamic optimisation of turbine cascade blades for high pressure stages of heavy duty gas turbines. This class of profiles features aerodynamic and geometric properties which can strongly depart from typical conditions of turbine profiles for aero engines applications. In fact, the Reynolds number and the trailing edge thickness of these profiles can be an order of magnitude higher than the correspondin...    »