A Unified Procedure for the Calculation of Off-Design Performance of Radial Turbomachinery

Abstract

An analytical technique is presented which permits calculating the off-design performance of radial, or mixed, flow centrifugal compressers and pumps. The method is based on the variation of blade loading diagrams as they are affected by the operating conditions of the machine. The influence of the changes of blade loading is expressed in terms of changes in the boundary layer momentum thickness in the internal flow passages. In turn the boundary layer thicknesses are expressed as a loss and as a flow acceleration in the critical passages such as the throat and the exit. The method makes use of no external arbitrary inputs except one relating to the development of the boundary layer thickness with the amount of fluid deceleration. The method was computerized and checked against five impellers and three diffusers. Acceptable agreement is found in the calculation of the shape of the characteristics and the location of the surge and choke points.