The impact of speed variation on the stability of variable speed axial compressors at efficient operating points

In the case of variable speed axial compressors, it is a matter of great importance to investigate the impact of speed variations on surge and stall transients. In spite of the important research on this subject, the qualitative behavior of variable speed axial compressors and the development of an effective controller are still challenging problems. The present paper studies the impact of speed transitions on the stability of high efficiency operating points being near to the fully developed rotating stall zone. Effects of throttle gain and acceleration rate as the bifurcation parameters of the model are also addressed to demonstrate the richness of nonlinear dynamics. Another key parameter, which affects the qualitative behavior of the system, is gas viscosity. The impact of gas viscosity is investigated as well. Time-domain simulation and bifurcation analysis as two standard and complementary methods for describing the qualitative behavior of systems are employed here. Outcomes reveal that speed transitions causing temporary stall harmonics, can drive the system to undesirable fully developed stall zone. This phenomenon threatens the stability of high efficiency operating points during speed transitions. Therefore, a need arises to develop an effective control approach being capable of simultaneously suppressing stall and achieving rapid acceleration.