A Reduced-Order Through-Flow Program for Choked and Cooled Axial Turbines

Abstract

A reduced-order through-flow program has been developed at the Lund Institute of Technology. The goal of the work was to develop and verify a program suitable for scientific studies of axial turbines. The program has built-in capability for multiple choked stages, and turbine cooling, as well as flexible modules for state, losses, deviation, and blockage. The code uses Matlab™ as a platform for numerics, pre- and post-processing. The turbine modules are available from the Institute free of charge for scientific use. Matlab is a commercially available mathematical package and is used as a numerical tool by many universities and companies. Today, several codes are available for turbine analysis at different levels. Most of the codes are proprietary and not available outside the companies that have developed them. There are, however, commercially available codes, but the user does not normally have accesses to the source code. This poses serious problems when such codes are used for scientific studies, and open easily modified code is indeed a desirable feature. The present paper describes in detail the calculation methods used to simulate performance of a cooled and choked turbine at off-design conditions. The algorithms necessary for finding the turbine choke point will, for example, be described in detail. The way in which the loss, deviation (including secondary and tip clearance), and blockage are included in a quasi 1-D calculation environment is also presented. The code is suitable for further development (e.g. streamline curvature through-flow), since it is based on modules for e.g. state, combustion, loss, deviation, diffuser, numerics, and in-and output data processing. It is fairly easy to transform the Matlab program into e.g. Fortran. However, the use of the original platform simplifies plotting of turbine characteristics, velocity triangles, etc. The program is validated against test-rig data from an industrial two-stage power turbine.