Coherent flow structures in a converging compound channel

摘要

This paper investigates the possible coexistence of the two kinds of momentum transfer observed in compound channels, that cause significant conveyance decrease, namely: (1) the turbulent interaction that develops in the shear layer between main channel and floodplains in a prismatic channel; and (2) the geometrical transfer due to cross-sectional changes in a non-prismatic channel. Experiments are performed in a symmetrically narrowing compound channel and focus on the behaviour of the shear layer along the transition between the prismatic and the non-prismatic reaches. A digital imaging technique enables to clearly identify horizontal turbulent structures in the upstream prismatic reach and to follow those structures when entering the converging reach. It is observed that the horizontal vortices are stretched as they are translated in the main channel and then quickly split into smaller scale structures that do not affect any more the conveyance.