Design and optimization of a multistage turbine for helium cooled reactor

This paper describes the aerodynamic design and explores the performance limits of a 600 MWt multistage helium turbine for a high temperature nuclear reactor closed cycle gas turbine. The design aims for maximum performance while limiting the number of stages for reasons of rotor dynamics and weight.A first part discusses the arguments that allow a preliminary selection of the overall dimensions by means of performance prediction correlations and simplified stress considerations. The rotational speed being fixed at 3000 rpm, the only degrees of freedom for the design are: the impeller diameter, number of stages and stage loading.The optimum load distribution of the different stages, the main flow parameters and the blade overall dimensions are defined by means of a 2D through-flow analysis method. The resulting absolute and relative flow angles and span-wise velocity variation are the input for a first detailed design by an inverse method. The latter defines the different 2D blade sections corresponding to prescribed optimum velocity distributions.The final 3D blade definition is made by means of a computer based 3D-DESIGN system developed at the von Karman Institute. This method combines a 3D Navier–Stokes (NS) solver, Database, Artificial Neural Network and Genetic Algorithm into a two level optimization technique for compressor and turbine stages. The use of 3D Navier–Stokes solvers allows full accounting of the secondary flow losses and optimization of the compound leaning of the stator vanes.The performance of the individual stages is used to define the multistage operating curves. The last part of the paper describes an evaluation of the cooling requirements of the first turbine rotor.