Author(s): Michele Trevisson; Olivier Eiff

Linked Author(s): Michele Trevisson, Olivier Eiff

Keywords: Secondary flows; Sediment ribbons; Large scale motions; Open channel flow

Abstract: Secondary flows of Prandtl's second kind are counterrotating flow cells driven by turbulence anisotropy in straight open or closed channel flows, in turn driven by geometric inhomogeneities like side walls. In wide open-channel flows, they are thus restricted to the wall regions, at least for smooth walls. In the presence of high relative bottom roughness (e.g. gravel) or sediment ribbons (Nezu, 1993), they have been found to cover the entire cross-section. While their topological characterization in relation to boundary conditions is quite clear (e.g. Nezu, 1993, Zampiron 2020), their generation mechanism over rough beds or with emerging ribbons is not. Here, we consider the case of sediment ribbons. Scherer (2022) showed recently that the formation of sediment ribbons over an initially uniform sediment bed is triggered by meandering outer-layer streaks. The interaction between emerging sediment ribbons and outer-layer streaks leads to a lateral locking and an elongation of the streaks. The aim of this work is to elucidate whether the locking of outer layer streaks can explain the formation of secondary flows, by measuring the secondary flow patterns as ribbons develop from a uniform fine-sediment bed.

DOI:

Year: 2025