Nonlinear analysis and control of rotating stall in axial flow compressors

Analysis and active control of stall instabilities in axial flow compressors are pursued using a combination of bifurcation analysis and nonlinear control. A low-order discretisation model of a PDE compressor model is found to exhibit a stationary (pitchfork) bifurcation at the onset of stall. Using 1D throttle opening (e.g. bleed valve) as a control, analysis of the linearized system at stall shows that the critical mode (zero eigenvalue) is unaffected by linear feedback. Hence, nonlinear stabilization techniques are necessary. A quadratic feedback control law is proposed based on the lower-order model and is found to adequately serve the control purposes for both the lower order and higher order discretizations.