Influences of radial migration flow on the compressor stage losses under low Reynolds number conditions

Radial migration flow structures on the blade suction surface in the rotor are commonly observed in transonic axial-flow fan/compressors. At sea level conditions, its intensity is relatively weak and causes very slight aerodynamic losses. However, under high-altitude low Reynolds number conditions, the radial migration flow will be significantly intensified. It will have strong interactions with other flow structures (such as shock wave, tip leakage flow, and wake) in the blade passage and lead to innegligible efficiency deficit in the entire compressor stage. To enhance the compressor performances at low Reynolds number conditions, it is crucial to achieve fundamental understandings of the origination, development, and downstream effects of radial migration flow. This paper conducted a detailed numerical investigation on the influences of radial migration flow near the rotor blade suction surface on the additional loss in a transonic compressor stage. The computational results confirm that under high-altitude conditions, radial migration flow is originated at the rotor blade hub corner and develops from the local separated flow and vortex. Its trajectory is largely determined by the interaction between the shock wave and the boundary layer flow, eventually mixing with the tip leakage flow and causing an accumulation of low-momentum flow near the casing. The migration of radial flow along the spanwise fraction interacts with the rotor blade wake and results in a larger total pressure and velocity deficit at the downstream stator inlet, deteriorating the aerodynamic loss in the stator blade. Meanwhile, the radial migration flow can be also triggered by the corner separation on the stator suction surface near the trailing edge, which exacerbates the local loss in the blade passage. Based on the features of radial migration flow, blade bend re-designs mainly near the hub and shroud ends have been applied to the rotor. It shows that the re-designed rotor has achieved an alleviated radial migration flow and a reduced wake zone at low Reynolds number conditions. Moreover, the re-designed compressor shows a notable higher adiabatic efficiency than the baseline one over the entire operating range, while the total pressure ratio and stable operating range are not sacrificed.