The above picture is a visualization from a numerical simulation of flow in a turbulent channel with its lower wall mounted with riblets; here, a near-wall region of the smooth, upper wall is shown. The Reynolds number based on skin-friction velocity is 145, and the corresponding wall unit spacing for the spanwise and streamwise directions are shown in the plot. These computations were done using a spectral-element/Fourier method on 32 nodes of the IBM SP2 at the Cornell Theory Center.
A "rake" of vortex lines (shown in blue) are plotted with each line beginning at a level of y+ = 10. We note the presence of a coherent, omega-like structure in the middle of this visualization as well as a smaller structure at the spanwise-edge of the domain.
In this visualization the rake of vortex lines are plotted at a starting level of y+ = 7 for a different time snapshot of the simulation. Here we see the presence of the classical hairpin structure at the smooth wall. Currently we are investigating the dynamics and morphology of the hairpin and omega structures as well as their relationship to shear stress production at the wall.