Large-eddy simulations of longitudinal vortices embedded in a turbulent boundary layer

Abstract

Large-eddy simulations of pairs of artificially generated longitudinal vortices embedded in a two-dimensional turbulent boundary layer are performed to study the dynamics of the vortical structures and to provide the unsteady inflow data for use in a future turbomachinery simulation. An immersed boundary method is employed to represent the wall-mounted half-delta wings that generate the counter-rotating vortex pairs. Two vortex pair configurations, with "common flow" between the vortices toward the end wall (common flow down) and away from the end wall (common flow up), respectively, are investigated. Mean velocities and Reynolds stresses compare well with experimental data, demonstrating the accuracy of the numerical approach and, in particular, the efficacy of immersed boundary treatment of the vortex generators. The large coherent vortices are characterized by streamwise velocity defect and negative mean pressure. The boundary layer in the common flow region is thinned by the vortices in the common-flow-down case and thickened by them in the common-flow-up case.