Effect of end zone boundary layer skew on secondary flow in high-lift turbine

The inlet boundary layer skew caused by rotor-stator interaction significantly influences the development of the secondary flow in high-lift low-pressure turbine. For high-lift low-pressure turbines used in civil turbofan engines, the method of combining experiment and numerical simulation was employed to investigate the influence mechanisms of inlet boundary layer skew on the development and evolution of secondary flows under wake sweep. Furthermore, the relative contributions of incoming wakes and boundary layer skew to secondary flow development were systematically quantified. The results indicate that, at an inlet Reynolds number of 1×10⁵ and turbulence intensity of 2.5%, endwall boundary layer skew reduces secondary flow and flow loss. This occurs by enhancing shear layer instability between the endwall-region fluid and the mainstream, while simultaneously weakening the transverse pressure gradient across the cascade channel. Increasing the rotational speed of the rotating endwall intensifies boundary layer skew, leading to thickening of the leading-edge boundary layer. This promotes secondary flow development and increases flow loss. Upstream wake further promotes shear layer instability, thereby weakening the secondary flow. However, the mixing dissipation associated with the wake adversely impacts the overall aerodynamic performance of the low-pressure turbine. At the position of 40% axial chord length downstream of the cascade, boundary layer skew reduces flow loss by approximately 3.45% compared to the baseline. Conversely, intensification of boundary layer skew increases flow loss by nearly 6.25%. The mixing dissipation from the upstream wake contributes a further flow loss increase of about 10.08% relative to the case with intensified skew.