ACTIVE STABILIZATION OF AXIAL COMPRESSORS WITH CIRCUMFERENTIAL INLET DISTORTION

This paper describes the first experimental validation of transfer fun ction modeling and active stabilization for axial compressors with cir cumferential inlet distortion. The inlet distortion experiments were c arried our in a three-stage low-speed compressor. Theory-experiment co mparisons of steady performance, unsteady stall precursor, and forced response (transfer function) data were all used to assess a control-th eoretic version of the Hynes-Greitzer distorted flow model. The tests showed good agreement between theory and data and demonstrated that a priori predictions, based on geometry and steady-state performance dat a, can be used to design control laws that stabilize rotating stall wi th inlet distortion. Based on these results, active feedback control h as been used to stabilize the inlet distortion induced instability ass ociated with rotating stall onset. The stabilization allowed stall-fre e operation to be extended below the natural (distorted flow) stall po int by lip to 3.7 percent for a 0.8 dynamic head distortion. For a 1.9 dynamic head distortion 40 percent of the mass flow range lost due to inlet distortion was regained through active control. The paper eluci dates the difficulties associated with active control with distortion, and introduces a new control law that addresses many of these challen ges.