Investigation On The Mechanism Of Effects Of Rotating Inlet Distortion On Compressor Aerodynamic Stability

The occurence of compressor flow instabilities limits the stable operating range of turbo engines. Therefore the compressor design must provide enough stall margin to eliminate the possibility of stall. However, inlet distortions may cause the flow throw the compressors to become unstable. For a twin-spool jet engine,if rotating stall occurs in the upstream compressor, the downstream compressor will work in the influence of the rotating stall cell, as called the rotating inlet distortion. This paper will investigate on the influence pattern of rotating inlet distortion to the compressor stability boundary and analyze the mechanism.The 2-D incompressible model which based on M-G model can calculate the axial-flow compression system stall transients under uniform and nonuniform inlet conditions. A square wave rotating inlet distortion is added into the model so we can analyze the influence of distortion rotating speed, distortion amplitude and angle to the compression system stability quantitatively.Designed a rotating inlet distortion generator equipment which distortion angle is variable and carried out experiments on a two-stage low-speed axial-flow compressor with 90 deg, 30 deg, 15 deg distortion rotating in different speed. The experiments result revealed that the distortion rotating speed has great influence on the compressor aerodynamic stability. When distortion rotating in some special speed, the compressor stall margin decreased most and call this speed as “dangerous speed”. The “dangerous speed” is close to the fully developed stall cell propagate speed. Different distortion angle will not change the “dangerous speed”, it only reduces the stability boundary mass flow coefficients around the “dangerous speed” as distortion angle decreased and has no great influence on the stability boundary under other distortion rotating speed.A mechanism model for the influence of rotating inlet distortion on the compressor aerodynamic stability is proposed based on the calculation and experiments results. This mechanism model explained appropriately why the distortion rotating in “dangerous speed” affects the compressor stall margin most.