Research progress on intelligent control technology for aerodynamic stability of axial compressors based on stall warning

In the context of increasing performance and expanding the operational envelope of aero-engines, the limited stall margin provided by passive flow control has been shown to exacerbate the conflict between compressor loading and stable working. Intelligent control, centered on stall warning and active flow control, enables stall suppression without sacrificing performance, becoming one of the key technologies in highly loaded compression systems for intelligent engines. This paper reviews the research progress on stall warning and active flow control, respectively, following the principle of warning before action. First, the performances, underlying principles and influencing factors of three conventional stall warning methods (time-domain analysis, frequency-domain analysis, and time-frequency analysis) are summarized. Emerging stall warning approaches based on machine learning are introduced and compared with conventional techniques in terms of advantages and limitations. Subsequently, this paper compares the strengths and weaknesses of three active control strategies: inter-stage bleeding, variable stator vanes and tip injection. Particular emphasis is placed on reviewing recent advances in both steady and unsteady tip injection methods. The influences of design parameters and the underlying flow control mechanisms are analyzed. The advantages and the limitations of both injection types are compared. What's more, this paper further summarizes the engineering feasibility and obstacles of incorporating a tip injection system in an in-service engine. Finally, existing limitations and a prospective outlook on future developments in this field are presented.