An experimental investigation of a boundary current instability

SELECTED PAPERS OF THE INTERNATIONAL SYMPOSIUM ON SHALLOW FLOWS, 16–18 JUNE 2003, DELFT, THE NETHERLANDSShallow FlowsEdited by Gerhard H.Jirka, Institute for Hydromechanics, University of Karlsruhe, GermanyWim S.J.Uijttewaal, Environmental Fluid Mechanics Section, Delft University of Technology, The NetherlandsISBN 0­203­02732­9 Master e­book ISBNISBN ­ (OEB Format)ISBN 90 5809 700 5 (Print Edition)International audienceThis study deals with the instability of a surface boundary current maintained along a vertical lateral wall by the Coriolis force. The flowing water floats over a homogeneous denser layer. Experiments have been performed in the large “Coriolis” turntable (Grenoble, France). High resolution measurements of the horizontal velocity field, obtained by Particle Image Velocimetry (PIV), at different depths, bring consistent results to explain the mechanism of instability. We observe the formation of a counter­current in the homogeneous lower layer. Instability first develops in this lower layer, in the form of small vortices generated in the viscous layer near the wall. This is essentially a barotropic instability. In a second stage, a baroclinic instability develops, leading to the meandering of the surface current. This interpretation is supported by measurements of the growth rates and phase difference between both layers, compared with the simple two­layer model of baroclinic instability