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Diffusion and Dispersion in Compound Channels: The Role of Large Scale Turbulent Structures

Author(s): Q. Fraselle; D. Bousmar; Y. Zech

Linked Author(s): Didier Bousmar, Yves Zech

Keywords: Compound channels; Solute transport; Diffusion/dispersion processes; Vertical axis turbulent eddies; TELEMAC-2D

Abstract: In a compound channel laboratory flume, a tracer (Na Cl solution) was injected at successive positions in the main channel: results mainly show an expansion of solute more developed towards the floodplains than towards the main channel when injected in the shear layer, undoubtedly due to the strong turbulent structures observed in compound channels. Experimental concentrations for the different injection configurations are compared to numerical ones. A first numerical model relies on a three-dimensional numerical integration of a simplified solute transport equation, applied to the experimental velocity profiles. Fitting of the numerical results on experimental profiles is done through an adequate choice of anisotropic eddy diffusivities. The commercial CFD software TELEMAC-2D developed by EDF is also used with its solute transport module to provide estimated coefficients which give a global indication of the mixing intensities in the different regions of the compound cross section. This “global” turbulent diffusion is compared to a second type of numerical simulations where large scale turbulent structures are modelled explicitly using TELEMAC. Thereby, the role of these turbulent eddies in solute transport becomes more evident.


Year: 2010

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