The evolution of the flow topologies of 3D separations in the stator passage of an axial compressor stage

Flow separations in compressor blade passages are common and can cause significant flow blockage and losses production in some instances. Because of the measurement difficulties, most of the previous studies concerning the compressor 3D separations were conducted in cascades facilities. In this paper, 3D separation flows were studied in the stator of a low-speed compressor test facility. In order to find their evolutionary processes, oil flow visualizations were conducted at four compressor operating conditions from the design to near-stall conditions. The results showed that the corner separations appeared at even the design condition; however, they were so weak causing very slight flow blockage until the maximum static pressure rise condition arrived. By using topological analyses methods, exact 3D flow structures inside the stator passage were reconstructed and their flow mechanisms were analyzed. It was found that, as the mass flow rate decreased, the flow topologies of 3D separations became much more complex and the evolutionary processes of the 3D flows were significantly affected by both the flow-flow interactions inside the stator passage and the rotor-stator interactions between blade rows. However, the complicated 3D flow structures in the tested stator passage always consist with four basic types of flows: the corner vortex flow, the flow of the corner separation with/without the ring-like vortex, and the blade surface separation flow. Finally, the results obtained based on the topological analyses of the oil-flow visualization pictures were validated by using the measured results of stereoscopic particle image velocimetry.