A Method for Evaluating the Aerodynamic Stability of Multi-Stage Axial-Flow Compressors

Abstract

A new simple engineering parameter to evaluate the stability of multi-stage axial compressors has been derived. It is based on the stability analysis for a small circumferential disturbance imposed on the steady state flow field. The analytical model assumes that the flow field is two dimensional and incompressible in the ducts between blade rows although the steady state density is permitted to change across the blade rows. The resulting stall parameter contains terms that relate to the slope of the pressure rise characteristic of the blade rows and the inertia effects of the fluid in the blade rows and ducts. The parameter leads to the classical stability criteria based on the slope of the overall total to static pressure rise coefficient in the limit where constant density and constant blade rotational speed are assumed across the compressor. The proposed stall parameter has been calculated for three different multi-stage axial flow compressors and the results indicate that the parameter has a strong correlation with the measured stability of the compressors. The good correlation with the test data demonstrates that the newly derived stall parameter captures much of the fundamental physics of instability inception in multi-stage compressors, and that it can be a good guideline for designers and engineers needing to evaluate the stability boundary of multi-stage machines.