A Method for Evaluating the Effect of Circumferential Inlet Distortion on the Aerodynamic Stability of Multi-Stage Axial-Flow Compressors

Abstract

A simple engineering parameter to evaluate the stability of high-speed multi-stage compressors with distorted inlet flow has been derived based on a simplified semi-compressible linear stability model. The parameter consists of steady-state flow quantities and geometric parameters of the compressor and it indicates that the circumferential integral of the slope of the steady-state individual blade row static pressure rise characteristics is important in the determination of the compressor stability limit in the presence of distortion. The parameter reduces to the author’s rotating stall inception parameter in the limit of non-distorted inlet flow. Since the model includes a downstream plenum and throttle, a condition for pure surge inception with undistorted inlet flow has been deduced. The pure surge conditions can be reduced to the classical dynamic and static instability conditions in the limit of a constant annulus area incompressible compressor. The results indicate that rotating stall always precedes surge instability, as many engineers and researchers would expect from experience. The parameter for instability with inlet distortion was calculated using test data measured in a high-speed 5-stage compressor with two different types of circumferential inlet distortion, and the results show that the parameter has a strong correlation with the data and is an improvement over the classical incompressible stability parameter. The results demonstrate that the parameter captures much of the physics important during the instability inception in a high-speed multi-stage compressor subjected to circumferential inlet distortion. The parameter clearly shows how each compressor component’s characteristics contribute to the overall stability in a high speed axial multi-stage compressor, therefore, it will aid engineers and designers in their understanding and prediction of the aerodynamic instability inception phenomena.