Author(s): N. Riviere; S. Gautier; E. Mignot

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Keywords: Open channel flow; Expansion; Recirculation; Confinement; Experiments

Abstract: The paper focuses on recirculation zones in open-channel flows. Such zones are of practical importance for river management, as they create slack flows, with silting, and shelters for wildlife. In open-channel flows, the behaviour of the recirculation zone is affected by the so-called vertical confinement effect between the free surface and the bed. The recirculation length follows two asymptotic regimes, frictional or non frictional, depending on the respective importance of the transverse and vertical shears accounted for by the bed friction number. This paper is based on laboratory experiments. It shows first the interaction between the reattachment location and the intermittent passing of large scale vortices advected along the recirculation. Second, it demonstrates that the recirculation length is also affected by the ability of the free-stream to keep its initial velocity. This ability is accounted for by the dimensionless aspect ratio of the expansion with an influence comparable to the one of the bed friction number.

DOI:

Year: 2011