STUDY ON UNSTEADY FLOW CHARACTERISTIC IN A TRANSONIC AXIAL COMPRESSOR ROTOR AT NEAR STALL CONDITION

In this paper, the three dimensional single-channel numerical simulation has been undertaken to analyze unsteady flow characteristic and fluctuation mechanism at near stall condition in a transonic compressor rotor. It has been found that at near stall condition, strong unsteady fluctuations appeared at the region near the downstream of shock wave and leading edge to 80% axial chord of blade pressure side in rotor tip. Then, detailed analysis of the tip flow field showed that the interaction between tip leakage vortex (TLV) and shock waves causes the spiral type breakdown of TLV, and caused reverse flow periodic shedding in the recirculation region, both of the effects given rise to the large fluctuation of the rotor tip field. Periodic shedding of the reverse flow affected the pressure distribution of blade pressure side so that the blade tip was unloaded and the tip leakage vortex breakdown was thus suppressed, thereby forming a self-sustaining unsteadiness. The TLV breakdown was the decisive factor leading to the flow unsteadiness.