Large-eddy simulation of turbulent boundary layers with embedded streamwise vortices

Abstract

The interaction of streamwise vortices with turbulent boundary layers has been investigated using largeeddy simulation. The initial conditions are a pair of counter-rotating, common flow down Oseen vortices superimposed on various instantaneous turbulent boundary layers. The time development of the vortices and their interaction with the boundary layer are studied by integrating the filtered Navier-Stokes equations in time. The most important effect of the vortices on the boundary layer is the thinning of the boundary layer between vortices (downwash region) and thickening of the boundary layer in the upwash region. The vortices mostly influence the structure of the outer layer while the inner layer is minimally affected. The vortices first move toward the wall as a result of the self-induced velocity, and then apart from each other due to the presence of image vortices at the solid wall. The Reynolds stress profiles highlight the highly three-dimensional structure of the turbulent boundary layer modified by the vortices. The presence of significant turbulent activity near the vortex center and in the upwash region suggests that localized instability mechanisms in addition to the convection of turbulent energy by secondary flow are responsible for this effect. High levels of turbulent kinetic energy and secondary stresses in the vicinity of the vortex center are also observed. The numerical results show good qualitative agreement with the experimental results of Pauleu and Eaton'. -