Rotating stall control in a high-speed stage with inlet distortion: Part I- Radial distortion

This paper presents the first attempt to stabilize rotating stall in a sing le-stage transonic axial flow compressor with inlet distortion using active feedback control. The experiments were conducted at the NASA Lewis Researc h Center on a single-stage transonic core compressor inlet stage. An annula r array of 12 jet-injectors located upstream of the rotor tip Was used for forced response testing and to extend the compressor stable operating range . Results for radial distortion are reported in this paper. First, the effe cts of radial distortion an the compressor performance and the dynamic beha vior were investigated. Control laws were designed using empirical transfer function estimates determined from forced response results. The transfer f unctions indicated that the compressor dynamics are decoupled with radial i nlet distortion, as they are for the case of undistorted inlet flow. Single -input-single-output (SISO) control strategies were therefore used for the radial distortion controller designs. Steady axisymmetric injection of 4 pe rcent of the compressor mass flow resulted in a reduction in stalling mass flow of 9.7 percent relative to the case with inlet distortion and no injec tion. Use of a robust H-alpha controller with unsteady nonaxisymmetric inje ction achieved a further reduction in stalling mass flow of 7.5 percent, re sulting in a total reduction of 17.2 percent.