Numerical Investigation of Low-Pressure Turbine Stage with Unsteady Wakes

Implicit large-eddy simulations of a 50% reaction linear low-pressure turbine stage with endwall were carried out for a chord-based Reynolds number of 50,000. The front-loaded high-lift L2F airfoil was chosen for both the stator vanes and rotor blades. Mean-flow visualizations for the upstream vanes reveal laminar separation from the suction surface at about thirty percent chord and a corner and passage vortex. The wakes shed by the vanes sweep over the suction surface of the downstream blades and suppress laminar separation away from the endwall. The vane passage vortex interacts with the leading edge of the blade where it intermittently aggravates a small pressure side leading edge separation. Once the passage vortex enters the rotor passage, the pitchwise velocity shear between the rotor blades causes it to be stretched strongly in the axial direction and to obtain a V-shape. The upper leg of the V-shaped structure, which is closer to the pressure side of the blade, is not only strengthened but also pushed towards the endwall by the secondary flow. Eventually it ends up as an elongated streamwise endwall structure near the pressure surface side trailing edge of the rotor blade. From there it is slowly traveling in the streamwise direction and out of the passage before it is replaced by the next streamwise endwall structure. The other leg of the V-shaped structure is dissipated.