Author(s): C. W. Li; J. H. Wang
Linked Author(s): Chi Wai Li
Keywords: Large Eddy Simulation; Scalar transport; Free surface flow
Abstract: Passive scalar, such as salinity and waste heat, often presents in ambient free surface water body and affects the water quality there. To accurately predict the turbulent transport of scalar a three-dimensional numerical model incorporating the method of Large Eddy Simulation has been developed. In this method the large scale turbulence is computed explicitly and the subgrid scale turbulence is modelled. The empiricism incurred for the specification of the dispersion and turbulent mixing coefficients is thus reduced to minimal. The governing equations are split into three parts in the finite difference solution: advection, dispersion and propagation. The advection part is solved by the QUICKEST scheme. The dispersion part is solved by the central difference method and the propagation part is solved implicitly by using the Gauss-Seidel iteration method. The model has been applied to simulate a continuous source in free surface channel flow. The computed results demonstrate the existence of the non-Fickian diffusion region close to the source. Further downstream the diffusion process obeys Fick' s Law and the computed results are in agreement with the analytical solution in which the magnitude of the diffusion coefficient is determined from physical experiments.