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Bed Friction and Transverse Fluxes of Momentum in a Shallow Flow over Inhomogeneous Rough Bed

Author(s): M. Rouzes; F. Y. Moulin; S. Cazin; M. Marchal; O. Eiff

Linked Author(s): Maxime Rouzès, Olivier Eiff

Keywords: Turbulence; Boundary layer; Mixing layer; Secondary flow; Shallow water flows

Abstract: Turbulent open-channel flows over a transverse discontinuity of roughness height were investigated experimentally for high relative submergenceα=h/Dequal to 0.33,0. 50 and 0.66 (where h is the roughness height and D the water depth). Stereoscopic Particle Image Velocimetry (SPIV) measurements were performed in longitudinal planes at different positions along the flow along the discontinuity and over one of the rough bed. For the turbulent boundary layer developed above the rough bed, we find that eventually, the roughness sublayer occupies the whole depth forα=0.66, but that a log law still exists even for this extremely confined flow. The roughness height ks is a function of both the roughness geometry andα, and its value decreases with increasingα. For the momentum fluxes through the roughness discontinuity, contributions from the secondary flow and the turbulent mixing are estimated for the flow above the roughness elements. Orders of magnitude are in accordance with previous studies but the development along the flume is non-trivial and requires further analysis.

DOI:

Year: 2016

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