Numerical Investigation of Freestream Turbulence Effect on Flow Through Low-Pressure Turbine Cascade

The low-pressure turbine drives the fan which produces the bulk thrust in modern high-bypass jet engines. Low-pressure turbines operate at low Reynolds numbers, which makes the flow susceptible to freestream turbulence. Large-eddy simulations of the flow through a linear low-pressure turbine cascade with front-loaded high-lift blades were carried out for a quiescent freestream and for a freestream turbulence intensity of 8%. The freestream turbulence was introduced with a Fourier mode-based model. For all cases, the endwall boundary layer was tripped to turbulence. Compared to the quiescent case, for the cases with freestream turbulence the suction side laminar separation and mass-averaged total pressure losses are strongly reduced. Freestream turbulence also affects the horseshoe vortex dynamics at the leading edge junction. Distortions of the convex suction surface boundary layer are interpreted as Klebanoff modes and streamwise vortices for the concave pressure side boundary layer are identified as Gortler vortices. For the case without freestream turbulence, the Klebanoff modes and Gortler vortices are missing.