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Focused on the structure and the unsteady characteristics of tip leakage flow, a numerical investigation of a transonic compressor rotor using detached-eddy simulation (DES) method is carried out. Details of the leakage vortex are better captured with DES method than RANS at different working conditions. At near stall point, it is clearly observed that interaction between tip leakage vortex and the bow shock leads to a vortex breakdown, which directly leads to the unsteadiness at the top region and also causes a blockage, which may further induce a spike-type stall inception. INTRODUCTION Tip leakage flow plays an important role in compressor rotors, which is closely related to loss (Denton, 1993) and stall (Vo, 2001) characteristics. As for low-speed compressors, flow structures as well as unsteadiness of tip leakage flow have been widely studied and certain achievements were obtained through numerical efforts and experiments. As the flow coefficient decreases, the interface between the tip leakage flow and the incoming flow moves upstream (Hoying et al., 1998), the trajectory of which will be aligned with the leading edge when the rotor finally encounters a spike-type stall (Vo et al., 2008). Vo came up with a criterion for spike-initiated numerical stall that leading-edge spillage and trailing-edge backflow are both essential, which was proved in low-speed compressor experiments (Deppe et al., 2008). Leading-edge spillage is later found to be an accompanying phenomenon, whose fundamental cause is the tornado-like vortex, resulted from the interaction between tip leakage vortex and leading-edge separation (Yamada et al., 2013). Moreover, attentions were also paid to flow structures and unsteady phenomena, for instance, the bubble-type breakdown of leakage vortex (Furukawa et al., 1998). With the increase of turbine requirements, the shaft speed of compressors is also increasing to achieve higher stage loading. Conclusions for tip leakage flow in low-speed compressors are not entirely suitable for transonic ones, due to greater pressure gradient and the existence of shock. The interaction between leakage vortex and the shock results in increasing complexity and less stability in the top flow field. Strong self-induced unsteadiness (Zhang et al., 2008; Biela et al., 2008; Du et al., 2013) was found in tip leakage flow with a characteristic frequency near 60% BPF (blade passing frequency). In addition, leakage vortex breakdown is revealed in transonic compressors, but in another form (Hofmann and Ballman, 2003; Yamada et al., 2004). Despite the efforts made by scholars in turbomachinary community, the mechanism of tip leakage flow as well as its self-induced unsteadiness are still not fully understood, especially in transonic compressors. Previous investigations have shown that unsteadiness of tip leakage flow is closely related to the interaction between shock and leakage vortex,

Unsteadiness of Tip Leakage Flow in the Detached-Eddy Simulation on a Transonic Compressor Rotor