Three-dimensional flow patterns at a river diffluence on the alluvial system of the Paraná River, Argentina

MORELL MI; TASSI PA; VIONNET CA

Chatou

Workshop; XVIIIth Telemac & Mascaret User Club; 2011

EDF R&D

P { text-indent: 0.2in; margin-bottom: 0.08in; direction: ltr; color: rgb(0, 0, 0); line-height: 95%; text-align: justify; widows: 2; orphans: 2; }P.western { font-family: "Times New Roman",serif; font-size: 10pt; }P.cjk { font-family: "Times New Roman",serif; font-size: 10pt; }P.ctl { font-family: "Times New Roman",serif; font-size: 10pt; }A.western:link { }A.ctl:link { }A:visited { color: rgb(128, 0, 128); }A.western:visited { }A.cjk:visited { }A.ctl:visited { } Whilst identification of secondary flows may be straightforward in open-channels with regular geometry and slowly varying plane curvature, it is not so in the case of natural meandering streams, whose boundaries are loose and irregular. Indeed, due to the continuously changing plan form and variable bed topography, the hydrodynamics of a natural meandering stream is rather complex. The flow field is strongly three-dimensional (3D), and in each cross-section of the meandering stream a cross-flow develops. Thus, on the basic flow there is superimposed a flow in the transverse direction which occupies the large part of the cross section, whose formation is understood in terms of the mechanical imbalance between the local elevation of the free surface and the centrifugal force induced by channel curvature. The behavior of the crosswise flow measured at the outlet of the Colastiné River, Argentina, where the flow diverts in two branches forming an almost T-shaped difluence, is briefly analyzed here with the open source code Telemac-3d. This communication reports the comparison of cross-flows captured with two acoustic Doppler current profiler (aDcp) in the study site against numerical solutions obtained with models of increasing complexity: i) hydrostatic 3D model, ii) full non-hydrostatic 3D model, in conjunction with the zero-equation and two-equations turbulence models.