NUMERICAL INVESTIGATIONS OF CROSS-FLOW EFFECTS ON SEPARATEDTRANSITION FLOW IN LOW-REYNOLDS-NUMBER COMPRESSOR CASCADE

At low Reynolds numbers (Re), intense secondary flows existin the compressor cascade corner region, which significantlydisturb the flow characteristics of the suction-side separatedshear layer and impact aerodynamic performance and flowstability. This study conducts Large Eddy Simulation (LES) onthe flow within a subsonic compressor cascade under low Reconditions (Re=2.5×10⁵), combined with the multiscale ProperOrthogonal Decomposition (mPOD) method, to systematicallyinvestigate the crossflow effects on the transition mechanisms ofthe suction-side separated shear layer. The results indicate thatthe crossflow substantially disrupts the spanwise coherence ofthe separated bubble, leading to the sequential appearance ofshort, medium, long, and secondary separation bubbles from theblade root to the midspan. Their evolution is directly governedby the path and intensity of the crossflow. In the near-endwallregion (z/H<0.14), the crossflow-induced vortex (CFIV)becomes the dominant structure. This vortex, generated by theinteraction between the crossflow jet and the separated shearlayer, promotes the downstream propagation of threedimensionaloblique waves, significantly altering the transitionprocess. Modal analysis of the turbulent kinetic energyproduction term (PTKE) reveals that the CFIV dominates PTKE atz/H < 0.14, whereas the K–H spanwise vortices play a primaryrole at z/H > 0.14. The transition boundary between thedominant mechanisms coincides with the location where thecrossflow fully enters the separation bubble. This study proposesa new model of "crossflow-induced transition", elucidating thespatial competition mechanism between crossflow and K–Hinstability. It not only provides a novel explanation for thetransition mechanism in the cascade corner region but alsooffers new insights for controlling compressor profile losses atlow Re, indicating that suppressing crossflow development is ascrucial as managing boundary layer separation.