Transition of stall routes in a high-load compressor under radial distorted inflow

The transition of stall routes under inlet radial distortion was experimentally studied in a high-load 1.5-stage axial compressor. Under uniform inflow condition, the stall precursor of the compressor is manifested as a modal wave type that the fluctuation of the tip leakage flow is weak. Although tip air injection that is fixed at the blade leading edge can increase the flow capacity in the tip region, the effect of stability-enhancing capability is poor. When suffering from inlet radial distortion, as the hub radial distortion, it can increase the flow capacity of the tip region that unloads the rotor blade tip, the stall precursor of the compressor is consistent with that under the uniform inflow condition, and tip air injection still cannot achieve significant stall margin improvement. However, under tip radial distortion, since it reduces the axial velocity and increases the angle of attack of incoming flow, thereby increasing the load at the blade tip, the stall precursor of compressor transits from the modal wave to the spike type. Thus, under the same injected mass flow ratio, tip air injection can delay the occurrence of stall by unloading the blade tip and suppressing the fluctuation of the leakage flow and that the stall margin can be improved more than twice compared with uniform inflow. However, when the injected mass flow increases to a certain extent, due to blade tip unload caused by tip air injection, the stall precursor transits back to the modal wave again, and the stall margin cannot be further improved. It fully explains the correlation between stall routes and the tip load, also confirms that tip air injection can only achieve stability-enhancing capability under strong tip loading and provides a guideline for its application in actual aero-engines.