Author(s): Toru Tanigawa, Adriano Coutinho de Lima

Linked Author(s): Adriano Coutinho de Lima

Keywords: Linear stability analysis; Horizontal organized vortex; Flow instability; Vegetation;

Abstract: Instability characteristics are studied for an open-channel flow which is partially covered with vegetation on both of its sides. Distinct from previous works, the base flow formulation is novel and consistently accounts for the distinction of two turbulence scales: 1) a large-scale turbulence associated with large-scale vortices centered near the velocity inflection points and 2) a small-scale turbulence associated with bed friction. The basic flow velocity profile resembles that of a confined jet flow. We analyse the effects of (1) bed friction, (2) kinematic eddy viscosity, (3) Froude number and (4) vegetation drag and density on the development of the large scale horizontal vortices, which appear near the edge of the vegetated zones. Our results indicate that two instability modes take place: a dominant mode, characterised by anti-phase vortex streets and a secondary mode characterized by in-phase vortex streets. The dominant mode is consistent with experiment observations whereas the secondary mode is overshadowed by the first mode.

DOI: https://doi.org/10.3850/38WC092019-1653

Year: 2019