Effect of distorted inflow on stall routes in a high-load compressor

The dynamic stall process under different distorted inflow conditions was experimentally investigated in a high-load 1.5-stage axial-flow compressor. Unsteady measurements indicate that under uniform inflow condition, the compressor exhibits modal-wave stall precursors, with negligible fluctuations in the tip leakage flow (TLF) and minimal stall margin improvement (SMI) from tip air injection. When suffering from circumferentially distorted inflow and the distorted intensity increases to a critical magnitude (DC60 = 0.785), the stall precursor transitions from modal-wave to spike type due to the continuous increase in blade tip loading. At this point, the unsteady fluctuations of the TLF become intense, and tip air injection demonstrates a significant SMI. As the injected mass flow increases to a certain level, the stall precursor reverts to modal-wave type, and further increases in injected mass flow do not significantly extend the stall limit. Under the rotational distortion inflow conditions, as the rotational speed of the distorted sector increases, the corresponding stall margin gradually decreases. When the rotational speed of distorted sector reaches 0.4 times the rotor speed, the stall margin decays most severely, and the stall precursor also transitions from modal-wave to spike type, with tip air injection exhibiting strong stall margin improvement. Unlike the circumferential distortion conditions, the stall precursor type remains spike type with further increasing injected mass flow due to the influence of the periodic perturbation of rotational distortion. It implies that the distorted inflow can alter the stall route, thus affecting the stability-enhancing capability in actual compressor. Meanwhile, tip air injection can only extend the stall limits of compressor with spiky stall precursors.