Stability control using tip air injection in an axial compressor subjected to rotating inlet distortion

Our present experimental investigation explores how tip air injection can improve the flow stability of a low-speed, single-stage axial compressor under rotating inlet distortion. The distortion was created using one or more 30° sector screens rotating at different speeds and directions. Measurements of total pressure downstream of the distorted inlet and unsteady wall pressures near the rotor tip were experimentally taken using probes and sensors placed upstream and around the rotor. Our results show that rotating inlet distortion reduces compressor flow stability, especially when the distortion rotates in the same direction as the rotor at about 0.4-0.5 times the rotor speed (or 0.4-0.5 rotor frequency). Under a single 30° co-rotating distortion at 0.5 times rotor speed, the stall flow coefficient increases by 13.4% while the stall pressure rise coefficient decreases by 22.0%, resulting in a 52.2% reduction in stall margin. To address this, tip air injection was used to extend the stall margin, and the improvement increased with higher injected mass flow ratio. With a single 30° co-rotating distortion at 0.5 rotor speed, the stable flow coefficient range is extended by 6.8%, 12.8%, and 21.5% as the injected mass flow ratio increases. Analysis of unsteady pressure data revealed that tip air injection helps prevent pre-stall disturbances from forming and spreading around the compressor, delaying stall development. It also weakens the interaction between the distortion rotation frequency and unsteady flows caused by leakage at the rotor tip. Overall, these effects boost the compressor stall margin under rotating inlet distortion, demonstrating that tip air injection is an effective method for enhancing flow stability in distorted flow conditions.