Breakdown of Streamwise Vortices near a Wall
Counter-rotating streamwise vortices within a laminar boundary layer were produced by a Görtler instability mechanism on a concave wall. Contour maps of constant streamwise velocity in the y–z plane normal to the mean flow revealed that the vortices produce strong distortions in the mean flow. Fluid was removed from the wall outward and produced regions where low speed fluid lay over higher momentum fluid. This highly unstable situation produced strongly inflectional profiles in both the normal and spanwise directions. Contour maps of the fluctuations suggest that the velocity oscillations are more closely related to the gradients in the spanwise direction rather than to the normal velocity gradient. The fluctuations broke down into turbulence at a Görtler number of approximately 9.
KeywordsVortex Vorticity Smoke Settling Rounded
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