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Turbulent transport in the outer region of rough-wall open-channel flows: the contribution of large coherent shear stress structures (LC3S)

HURTHER, D. ; LEMMIN, U. ; TERRAY, E. A.

In: Journal of Fluid Mechanics, 2007, vol. 574, p. 465-493

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    Title
    • Turbulent transport in the outer region of rough-wall open-channel flows: the contribution of large coherent shear stress structures (LC3S)
    Author
    • HURTHER, D.. Laboratoire des Ecoulements Géophysiques et Industriels, CNRS UMR 5519, Grenoble, 38041, France
    • LEMMIN, U.. Ecole Polytechnique Fédérale Lausanne, CH-1015 Lausanne, Switzerland
    • TERRAY, E. A.. Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
    Document Type
    • Postprint
    Classification
    • Engineering
    OAI-PMH Identifier
    • oai:doc.rero.ch:292468
    Summary
    Acoustic Doppler velocity profiler (ADVP) measurements of instantaneous three-dimensional velocity profiles over the entire turbulent boundary layer height, δ, of rough-bed open-channel flows at moderate Reynolds numbers show the presence of large scale coherent shear stress structures (called LC3S herein) in the zones of uniformly retarded streamwise momentum. LC3S events over streamwise distances of several boundary layer thicknesses dominate the mean shear dynamics. Polymodal histograms of short streamwise velocity samples confirm the subdivision of uniform streamwise momentum into three zones also observed by Adrian et al. (J. Fluid Mech., vol. 422, 2000, p. 1). The mean streamwise dimension of the zones varies between 1δ and 2.5δ. In the intermediate region (0.2