Tip air injection to extend stall margin of multi-stage axial flow compressor with inlet radial distortion

To prevent the deterioration of the inlet tip and hub radial distortion on stall margin, tip air injection was experimentally studied in a three-stage axial flow compressor. By generating a total pressure distortion intensity of 16.8% and 8.6%, the inlet tip and hub radial distortion can obtain stall margin variation of -5.1% and 10.5%, respectively. With the help of time-resolved pressure transducers installed on the casing wall and five-hole probes installed downstream of each rotor blade row, the unsteady measurement results demonstrate that the first stage stalls first under different inflow conditions and only the unsteady tip leakage flow at the first stage becomes stronger near the stall limit. Therefore, tip air injection is applied at the first stage under the distorted inflow to ensure the stable operation. Under inlet tip radial distortion, which strengths the unsteady tip leakage flow and blade tip separation reflected by the outlet axial velocity and flow angle, tip air injection can weaken the unsteady tip leakage flow, and remove the tip separation at the first stage, thereby making the second stage stall first such that only stall margin improvement of 19.2% can be obtained compared with uniform inflow. Although hub radial distortion can delay the occurrence of stall by weakening unsteady tip leakage flow and increasing the tip flow capability, overlarge injection can still improve the stall margin by 20.5% through further weakening the unsteady tip leakage flow and reducing the blade tip separation.