Numerical Simulation of Turbulent Boundary Layer with Free Stream Turbulence

Abstract

Front-loaded high-lift low-pressure turbine blades suffer from increased endwall losses compared to more traditional moderate-lift blades. The effect of freestream turbulence on the endwall losses has not been investigated in great detail. As a first step towards the simulation of a front-loaded high-lift low-pressure turbine cascade with freestream turbulence, large-eddy simulations of the approach boundary layer with freestream turbulence were carried out. These simulations provide guidance regarding the selection of the grid resolution and the freestream turbulence intensity and integral turbulence length scale. The approach flow simulations established sufficient confidence in the approach to proceed with first large-eddy simulations of the flow through a linear cascade with L2F airfoils. For one of the two simulations, both the endwall boundary layer and the freestream were turbulent. For the other simulation, the endwall boundary layer was turbulent and the freestream was quiescent (no freestream turbulence). A detailed comparison of the two cases reveals a stronger passage vortex and weaker suction surface laminar separation for the case with freestream turbulence.