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. A comparison of the optimisation results and the reference turbine cascades attests the high potential of the developed procedure. 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. 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. The main optimisation target in this work was the reduction of the cascade total pressure losses by fixing the 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. In fact, a major goal of the present work was the development of an aerodynamic 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 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 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.    «

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...    »