Streamwise vortices in plane mixing layers originating from laminar or turbulent initial conditions

Large Eddy Simulations of the plane mixing layer have been performed, for the purpose of educing the streamwise vortex structure that may exist in these flows. Both an initially-laminar and initially-turbulent mixing layer are considered in this study. The initially-laminar flow originates from Blasius profiles with a white noise fluctuation environment, whilst the initially turbulent flow has an inflow condition obtained from an inflow turbulence
generation method. Both simulations produce good mean flow statistics when compared with reference experimental data. The simulations capture the change in growth rate when the initial conditions are either laminar or turbulent. Flow visualisation images demonstrate that both mixing layers contain organised turbulent coherent structures, and that the structures contain rows of streamwise vortices distributed across the span of the mixing layer. Ensemble averaging of the cross-plane data, however, shows no evidence for statistically stationary streamwise vortices in either simulation.