Active control of multistage axial-compressor aerodynamic instabilities has been studied analytically using a blade-row by blade-row compression system model. The instabilities considered are those which result from a global system instability. The control approach taken is to suppress the instability by actively changing the system damping characteristics. This was accomplished by varying dynamically the compressor stage characteristics to extend the region of the compression system operation. Specifically, the stator row of a compressor stage is actively dithered based on its inlet or exit pressure fluctuation measurement such that the stage characteristics are modified in such a way to improve the overall system stability.
The analytical model and the results of the stator dither study are presented in this paper. The results indicated a slight gain in the compressor stability limit line when the compressor stages are well matched. With increased interstage bleed, resulting in a mismatch between the front and the rear blocks of the compressor, the stabilization results indicated a significant gain in the stability limit line. In addition, the stator selection studies showed the importance of locating the active action near to and upstream of the stage where the system instability initiates.