An Investigation Of Effects Of Rotating Total Pressure Distortion On Aerodynamic Stability Of Compressors

The useful operating range of compressors is limited by the onset of aerodynamic instabilities in them. The instabilities will degrade compressor performance and durability, and traditionally, this undesirable behavior has been avoided by operating the compressor with a safe margin from the instability onset point,the so-called"surge margin". But the problem is that the requirement for the surge margin will reduce the available pressure rise and the achievable efficiency, because the peak efficiency region is normally quite close to the surge line, so that a good design of compressor must achieve the balance between performance and aerodynamic stability. With the development of design technology and theory of compressors, it is very importand,at present, to develop the theory and technology about aerodynamic stability in compressors. In this paper, numerical simulation and experimental test have been carried out to investigate the post stall transient behavior and the onset of aerodynamic instabilities in axial compression systems both with uniform inlet flow and with rotating inlet total pressure distortion.Firstly, based on the theory developed by Moore and Greitzer, a new simplifying approximation is proposed to get a simplified model of post stall transients inaxial compression systems with rotating inlet total pressure distortion, and calculations are presented to predict the post stall transient behavior and the onset of flow instabilities in axial compression systems with and without rotating inlet total pressure distortion. It has been found that both the inlet distortion amplitude and rotating speed have a strong effect on the stability and post stall transient behavior of a compression system, and the rotating speed has similar effect on rotating stall boundary and suege boundary of a compressor. But the resonant response frequency strongly depends on the frequency at which the stall cell rotates. Some qualitative comparisons with available experimental results are made, and show that the model and results are reliable.Secondly, a nonlinear multi"actuator disk"model is proposed to analyze the dynamic behavior of aerodynamic instabilities in high speed multistage axial compressors for both cases with and without rotating inlet distortion. The model describes the duct flow fields using two dimensional, compressible and unsteady Euler equations, and accounts for the influences of downstream plenum and throttle in the system as well. It replaces each blade row of compressors with a disk. The main purpose of this work is to predict the mechanism of two dimensional short wavelength rotating stall inception, and the interaction between blade rows in high speed multistage compressors, and the influence of rotating speed of inlet totatl pressure distortion on the onset of flow instability.Lastly, effects of rotating inlet distortion on the aerodynamic stability of compressor are carried out in a 2-stage low speed compressor. The stable and rotating stall characteristics of the compressure and the effect of rotating speed of inlet distortion are analyzed in detail experimentally. The results show that the rotating screen in the upstream has large impact on the aerodynamic stability and total-to-static pressure rise of the compressor. When rotating screen rotates at counter direction with the rotor, the deficits of stability and pressure rise ratio are negligible. For the case of corotating distortion, the speed of the rotating screen has strong effects on both the stability and the pressure rise, especially between 40-60 percent of rotor speed. Through the research on the variation of amplitude of characteristic frequency, it is concluded that the rotating stall cell called rotating-screen-induced rotating stall in this paper, induced by the low-total-pressure area produced by rotating screen, appears in the compressor first. If the mass flow continues to decrease, the nature rotating stall cell will turn on, and the inchoate stall cell will disappear. The stall inception process of this experiment reveals that the rotating screen can't affect the kind of the stall inception.