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Numerical analysis of the effluent dispersion in rivers with different longitudinal diffusion coefficients
Author(s): Almir Guilherme Siqueira Lopes Ritta, Thiago Roberto Almeida, Julio Tomás Aquije Chacaltana, Roger Matsumoto Moreira
Keywords: Computational fluid dynamics, CFD, Longitudinal diffusion coefficient, Parametric equations
The knowledge of pollutant dispersion in water bodies is a matter of concern in water quality control, especially when a new industrial development will be installing e.g. near the river margins. As it is known, dispersion has great influence on the spread of pollutant mass into the water body. Therefore, the purpose of this paper is to analyse the influence of the longitudinal dispersion coefficient (E) on the transport of a conservative pollutant in rivers and channels via CFD (Computational Fluid Dynamics). Different parametric equations for the longitudinal dispersion coefficient (E) are investigated in this study. The dispersion of the pollutant is carried out by a scalar advection-diffusion transport equation that represents the conservation of the mass of the pollutant. The hydrodynamics are solved using the Navier-Stokes equations and the continuity equation for the velocity field considering the fluid as incompressible. For the unidimensional and two-dimensional cases, the numerical results of the dispersion of pollutants are compared with those obtained by analytical models present in the literature. The concentration field, over time and space, showed significant differences of concentration peak and arrival time of the plume depending on the model used to calculate E. In order to validate the performed simulations, 2D numerical results for channel are compared with the experimental data from Modenesi et al. (2004). Such analyses were necessary to establish an appropriate correlation between the simulated channels and the real channels. The use of different parametrizations for the longitudinal dispersion coefficient in a 2D channel reveals significant differences of peak concentration and arrival time of the plume. As expected, the numerical results of the transport of pollutants show the dependence on the parameterization of the longitudinal dispersion coefficient. And the one that best represents the distribution of pollutants is that proposed by Kashfipour & Falconer.