Controlling secondary flow in high-lift low-pressure turbine using boundary-layer slot suction

The design of high-lift Low-Pressure Turbines (LPTs) causes the separation of the boundary layer on the suction side of the blade and leads to a strong secondary flow. This present study aims to minimize secondary losses through endwall slot suction and incoming wakes in a front-loaded high-lift LPT cascade with Zweifel of 1.58 under low Reynolds number of 25000. Two slotted schemes for the boundary layer of the endwall were designed (Plan A and Plan B), and the effects of suction mass flow on secondary flow were studied. The underlying physics of the endwall boundary layer of the suction and secondary flow under unsteady wakes was discussed. The results show that slot suction at the endwall boundary layer can significantly suppress the secondary flow by removing low-momentum fluids. Plans A and B significantly reduced the secondary kinetic energy by 44.2% and 36.9%, respectively, compared with the baseline cascade at the suction mass flow ratios of 1%. With an increase in the mass flow ratio of suction, the secondary flow was gradually reduced in both Plans A and B. It is more beneficial to control the secondary flow to destroy the intersection of the pressure side and suction side of the horseshoe vortex before it develops into a passage vortex. Under unsteady wakes, the combined effects of incoming wakes and endwall boundary layer suction can further suppress the secondary flow at the suction mass flow ratios of 2% for Plan A, because the positive and negative vorticity inside upstream wakes accelerated the mixing of the main flow and secondary flow and thus increased the energy of secondary vortices.