PREDICTION OF STALL MARGIN FOR MULTISTAGE AXIAL FLOW COMPRESSORS

Two methods for predicting the onset of rotating stall in multistage axial flow compressors are provided in this paper.First,the semi-empirical criterion about the isolated blade row is extended to the analysis of the multistage axial flow compressors.The downstream condition of preceding stage is considered as the upstream one of next stage and similar calculation is made for every stage.By comparison of the flows for each unit at the onset of rotating stall,the stall margin of the multistage compressor can be determined.The results of prediction agree with the experimental data fairly well.Secondly,with the help of the unsteady two-dimensional incompressible flow model,the inception criterion of rotating stall for a double stages axial flow compressor is derived in detail according to a small disturbance stability theory.Characteristic equation is solved iteratively using a Newton-Raphson scheme.Some numerical examples have been predicted with the aid of the written computer codes.Good agreement between the analytical and experimental results indicates that the analysis is believable.The variations of damping factor under the different conditions are compared and the rate of loss variation is analysed as inlet relative airflow angle increases for each blade row.The above-mentioned two approaches both can be used to predict the stall margin for subsonic and transonic multistage axial flow compressors.