Pollutant Dispersion Model in a Two-dimensional Street Canyons Using Computational Fluid Dynamics

A two-dimensional model is applied to simulate the wind speed and temperature distributions and pollutants dispersion within an isolated street canyon using SIMPLE algorithm in ANSYS Fluent version 16.2. The simulation is based on the Reynolds-averaged Navier–Stokes equations coupled with a series of standard, RNG and realizable ? − ? turbulence models. Simulation domain consisted of a street canyon with two buildings enclosing a street and urban environment with the aspect ratio of 1. The wind is assumed to be perpendicular to the direction of the street and the source of the pollution is assumed to be liner. The results indicated that the RNG ? − ? turbulence model is the most optimum model by comparing with the calculated data under different wind speed patterns. The improvement of turbulent viscosity term of the RNG ? − ? turbulence model provides a more accurate and reliable numerical solution for the present study regarding to the pollution dispersion in a street canyon. The simulation results also indicated that the dimensionless pollutant concentrations, K, is larger on the leeward side of the buildings and decrease exponentially from bottom, floor to top of the upstream buildings, while on the windward side are almost constant along the height of downstream buildings. Furthermore, the pollutant concentrations on the leeward side are more than that on the windward side due to the pollutant transportation of vortex circulation

Keywords:

Pollutant dispersion model , street canyon , computational fluid dynamics , Reynolds-averaged Navier–Stokes equations