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 here providing new insights into such questions as why both one and two-legged hairpins appear, why and how low-speed streaks form and why they persist, why hairpin-like rotational regions form, and why mushroom-like shapes and “pockets” are found in smoke visualizations of boundary layers. Consideration of the relationship between vortex furrows and the complex vortical structures appearing within the fully turbulent zone provides some insights into why turbulence in the boundary layer is self-sustaining.