The Off-Design Analysis of Axial-Flow Compressors

Abstract

This paper describes in some detail the methods used for generation of a computer program for analyzing the off-design performance of axial compressors. The purpose of the study was to predict such axial-compressor characteristics as pressure rise and efficiency as a junction of mass flow and rotor speed when only the mechanical geometry of the annulus and blades are given. The aerodynamic analysis is divided into two basic parts. The first part of the analysis involves the numerical solution of the equations of motion in the compressor to find the flow field, temperature and pressure rise, and efficiency of the compressor. The second part concerns the analysis of the blade elements, in particular their performance at various angles of attack. Several effects are included that have a bearing on this performance. The relative Mach number and the axial-velocity ratio across the blade element, together with the shape of the blade and its configuration in the compressor, affect the flow discharging from the blade. Therefore, an elaborate study has been included to find the flow angle at the blade discharge and the pressure losses of the flow passing through the blade row. The calculation procedures have been tested by applying them to a number of compressors for which sufficient experimental data were available. A one-stage, a two-stage transonic, and a 13-stage axial compressor have been investigated and good agreement with experiments has been found provided the correct boundary layer displacement thickness along the annulus wall is used.