Vortex Dynamics in Transitional and Turbulent Boundary Layers

The dynamics of transitional and turbulent boundary layers is explored via a hybrid vortex filament/finite volume simulation scheme in which vortical structures are identified without the constraints imposed by the traditional assumption that they are synonymous with rotational regions. Vortex furrows consisting of elongated, streamwise-oriented, raised perturbations to the wall vorticity layer overlying low-speed streaks are found to be the principal structural element appearing during the Klebanoff-type transition. A number of dynamical properties of the furrows are considered, providing new insights into such questions as why hairpinlike rotational regions form that occur both singly and in pairs, why and how low-speed streaks form and why they persist, and why mushroomlike shapes and pockets are found in smoke visualizations of boundary layers. The physical picture of the boundary layer that emerges from the consideration of the dynamics of the vortex furrows provides some insights into why turbulence in the boundary layer is self-sustaining.