New aspects of turbulent boundary-layer structure
- 1 June 1981
- journal article
- research article
- Published by Cambridge University Press (CUP) in Journal of Fluid Mechanics
- Vol. 107 (-1), 297-338
- https://doi.org/10.1017/s0022112081001791
Abstract
Flow visualization studies of the zero-pressure-gradient turbulent boundary layer over the Reynolds-number range 500 < Reθ < 17500 have shown large Reynolds-number effects on boundary-layer structure.At high Reynolds numbers (Reθ > 2000, say) the layer appears to consist very largely of elongated hairpin vortices or vortex pairs, originating in the wall region and extending through a large part of the boundary-layer thickness or beyond it; they are for the most part inclined to the wall at a characteristic angle in the region of 40–50°. Large-scale features, which exhibit a slow overturning motion, appear to consist mainly of random arrays of such hairpin vortices, although there is some evidence of more systematic structures.At low Reynolds numbers (Reθ < 800, say) the hairpin vortices are very much less elongated and are better described as horseshoe vortices or vortex loops; large-scale features now consist simply of isolated vortex loops (at the very lowest Reynolds numbers), or of several such loops interacting strongly, and show a relatively brisk rate of rotation.Keywords
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