Numerical Investigation of 50% Reaction Low-Pressure Turbine Stage

A large-eddy simulation of a fifty percent reaction linear low-pressure turbine stage with front-loaded high-lift airfoils was carried out for a Reynolds number based on axial chord of 100,000. The spanwise extent of the airfoils was two times the axial chord and the endwall boundary layer thickness upstream of the stage was matched to wind tunnel measurements at the Air Force Research Laboratory. The endwall flow topology for the stator vanes is similar to that observed in linear cascade experiments and features a passage vortex as dominant flow structure. The turbulent wakes of the stator vanes pass over the downstream rotor blades where they transition the suction surface boundary layer and diminish the laminar separation. The wakes also considerably weaken the rotor secondary flow, passage vortex and corner separation. A new endwall flow structure is identified near the pressure-side trailing edge of the rotor blades. The time-dependent rotor flow data were analyzed with the proper orthogonal decomposition and spectral proper orthogonal decomposition. The unsteady wakes are captured by modes with twice and thrice the wake-passing frequency. Significant interaction of the wakes with the corner separation takes place at the wake-passing frequency and at three times the wake-passing frequency. The present results are encouraging as they suggest that the elevated endwall losses for high-lift front-loaded low-pressure turbine profiles maybe partially alleviated by the passing wakes.