Review of tip air injection to improve stall margin in axial compressors

The present paper provides a summary of investigations of the tip air injection, which has been studied for over 30 years to extend the stall margin in axial flow compressors. The review covers the design of injected parameters, understanding of stability-enhancing mechanism, application of active control, and self-recirculation based on tip air injection. First, the injected parameters that can influence the stability-enhancing capability are surveyed and classified. These include injected mass flow and momentum, structure, pitch and yaw angle, axial location, and circumferential distribution. Next, the effect of tip air injection on the internal flow field is introduced; the action on the main stream flow or tip leakage flow depends on the injected moment ratio. Finally, the applications of active control with tip air injection and self-recirculating injection from a single-rotor to multi-stage compressors are listed and discussed. The active control methods are based on the Moore-Greitzer model and online prediction of stall inception. This study aims to aid researchers who are working on stability enhancement with tip air injection in compressors to improve their work. Moreover, considering that the regulation of injected mass flows or momentums is flexible, this study would facilitate the immediate application of the tip air injection in actual aero-engine compressors.