New concepts for active control of rotating stall and surge

Flow instabilities in transonic compressors include rotating stall and surge. Air Injection control has been demonstrated to be an effective strategy for actively suppressing rotating stall and surge. In industrial applications such as aero-engines, the implementation of air injection control schemes is constrained by factors such as the "cost" in terms of efficiency lost and availability of high pressure air, and the size and weight of the actuation system. Air will typically be re-circulated from a downstream compressor stage. The challenge, then, is to create control schemes that achieve acceptable performance with less air and fewer actuators. In this paper, new control concepts to address these implementation challenges in active control of rotating stall and surge are presented. The single-sided injection control scheme was used to reduce the net mass injected, notch-based control strategy was used to provide a framework for implementing nonlinear controllers to high speed compressors, and control laws that incorporate the discrete nature of the actuators are used to reduce the number of actuators. Results from experimental validation with data from high speed compressors are presented.