Imbedded Longitudinal Vortices in Turbulent Boundary Layers
Sufficiently strong lateral deflection (“skewing”) of the mean streamlines in a shear layer can lead to the generation of discrete longitudinal vortices. The mechanism is basically in viscid, given the presence of an initial shear: this “skew-induced” vorticity should be distinguished from the generation of streamwise vorticity by Reynolds stresses, which is important only in very long, straight streamwise corners and is confined in practice to noncircular ducts. In most cases of practical interest the boundary layer and the imbedded vortex will be turbulent but the decay of the vortex under the action of Reynolds stresses is slow, because its circulation is reduced only by the effect of the spanwise component of skin friction. That is, the skew-induced vortices can influence the flow for a very long distance downstream. The present paper is a description of measurements of the mean and turbulent properties of decaying vortices and vortex pairs; the process of formation (being “ in viscid “) does not require such detailed study as the slow decay. The configurations used are idealizations of those found in practice, but the data should be useful for developing and testing calculation methods intended for reallife cases.
KeywordsReynolds Stress Turbulent Boundary Layer Eddy Viscosity Vortex Pair Vortex Generator
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