Axial turbine preliminary design optimization

Osmar F. R. Silva, J. T. Tomita, C. Bringhenti, D. F. Cavalva (Aeronautics Institute of Technology)

CHALLENGE - The turbomachinery design process consists of several steps in order to obtain a final and optimized machine geometry. The design process handles many geometrical parameters: space-chord-ratio, aspect ratio, hub-to-tip ratio, and so on. This study deals with a preliminary design process of a single stage axial flow turbine using loss model correlations coupled to a multi-objective optimization process.

SOLUTION - The simulation was proposed to investigate the axial flow turbine used in the process of design of a single-shaft turbojet. The commercial software Axial NRec was used for the development of the turbomachinery design. The velocity triangles are calculated in the inlet and outlet, after that the croqui and the 3D geometry was generated. The optimization process was realized using a type of genetic algorithm NSGA-II run in optimization software modeFRONTIER. The use of this class of algorithm for optimization was based on the turbomachinery design complexity and due to the nonlinearity of the variables involved during the process.

BENEFITS - The simulation results show new possibilities of variable arrangements by varying blade and stator angles at mid and tip span to achieve maximum isentropic efficiency of the axial turbine. Improvement of efficiency is reached, with new arrangement of blade angles allowing better flow alignment and deflection on the blade surface. The highest efficiency is for beta angle between 13 to 15 degrees in the mid span. The optimized angles provide a new velocity distribution, so the velocity triangles in the Rotor outlet were modified.