Numerical investigation of near-stall behavior of a transonic compressor stage under 80% nominal speed condition

In this paper, steady simulations, unsteady simulations, fluid and structure interaction (FSI) simulations are respectively performed to investigate the near-stall behavior of a transonic compressor stage under 80% nominal speed condition. The corresponding near-stall simulations at 100% nominal speed are also carried out as necessary comparisons. Steady analyses show that, under 80% nominal speed condition, a separation vortex (SV) caused by high incidence is located near suction side of rotor blade on about 80% blade span. When flowing downstream, the SV is not confined near the suction side, it instead diffuses into main flow and generates blockage. Unsteady simulations demonstrate that a motive low pressure zone is induced by an unsteady SV, a specific type of flow instability. The motive low pressure zone leads to violent blade loading fluctuations. Unsteady analyses also show that there is an interaction between SV and tip leakage vortex (TLV) which possess a same characteristic frequency. The interaction is strong in downstream positions of rotor passages, whereas weak in upstream positions. FSI simulations reveal that, as a result of the violent instability of SV and TLV at 80% nominal speed, the blade oscillation is more drastic than that at 100% nominal speed.