Vortex Filament Simulation of the Turbulent Boundary Layer

A hybrid vortex filament scheme with the capability of simulating bounded turbulent flows is described. Viscous generation of new vortex elements at solid surfaces is accomplished through the intermediary step of solving the viscous vorticity transport equation on a thin boundary mesh via a finite difference and finite volume method. The transitional and turbulent boundary-layer flow past a wide, finite thickness, flat plate with rounded edges is computed with a view toward validating the methodology and gaining new insight into the structural aspects of transition. The predicted mean velocity and related statistics are well matched to experimental and numerical data. The representation of the flow through vortex filaments reveals that a distinction needs to be made between vortical structures, on one hand, and the rotational motion that they produce in the flowfield, on the other hand. In particular, hairpin-shaped regions that are commonly found by vortex identification schemes are found to not be structures in their own right, but rather the rotational signature of raised furrows in the surface vortex sheet. The latter overlie low-speed streaks and evolve to include ejected mushroom-shaped structures as well as spanwise vortices associated with roll-up.