Eulerian RANS simulation of pollutant dispersion in atmospheric boundary layer considering anisotropic and near-source diffusivity behavior

This study proposes an anisotropic concentration diffusivity model in the Reynolds-averaged Navier-Stokes equations (RANS) and the Eulerian dispersion model. The proposed model combines models to consider the turbulent anisotropic and near-source limited diffusivity based on the generalized gradient-diffusion hypothesis and travel time. The proposed model and conventional isotropic models were applied to predict the pollutant dispersion in an atmospheric boundary layer from elevated and ground-level sources. The predicted concentration profile and plume half-width were validated with a previous wind tunnel experiment in the literature. Both the proposed and isotropic models using the diffusivity limiter accurately predicted the mean concentration profiles at the central vertical plane. The isotropic models did not accurately predict the horizontal and vertical plume widths of the ground-level source while the proposed model successfully predicted those. The equivalent turbulent Schmidt numbers in the proposed model differed in each direction. The proposed model predicted counter-gradient turbulent diffusion in the streamwise direction. In addition, accurate Reynolds stress was found to be crucial for reproducing the anisotropic concentration diffusivity in the proposed model.