Analysis of near-tip unsteady flowfield in a transonic compressor rotor at near stall condition

Three-dimensional single-passage steady and unsteady simulations were carried out to investigate the flowfield in a transonic compressor rotor (Rotor 35). Via comparing the steady predicted results with the available experimental data, it turned out that, in addition to matching the total performance map well, the predicted results also captured the trend of development of tip leakage vortex (TLV) reasonably well. The further unsteady calculation at near stall condition showed that the tip leakage flow without rolling up into TLV, encountered the incoming flow and then interacted with the low-energy area due to the breakdown of TLV, thus leading to the formation of tip secondary vortex (TSV). With the rearward movement of TSV, its location and associated blockage resulted in cyclic variation in near-tip blade loading, which in turn lead to the occurrence of a periodic self-sustained unsteady flow phenomenon in near-tip passage.