Numerical Simulation of the Distribution of Vehicle Emissions in a Street Canyon

The results of mathematical modeling of a nonisothermal turbulent air flow and admixture transport in an idealized street canyon are presented. The simulation is based on the RANS model, numerical algorithm, and application package developed by the authors, which are improved to take into account the effect of the buoyancy force on the aerodynamics and admixture transport. The mathematical model includes Reynolds-averaged stationary three-dimensional Navier–Stokes equations, as well as equations of heat transfer and impurity transport. For closing, a k-eps turbulence model is chosen taking into account the buoyancy forces. The numerical algorithm uses the finite volume method, nonuniform structured grids, and the fictitious domain method. The differential problem is approximated using Van Leer’s monotonized linear upwind scheme and piecewise linear interpolation for dependent quantities. The resulting grid equations are solved sequentially by N.I. Buleev’s iterative method. The SIMPLE algorithm is used to match the velocity and pressure fields. Using the developed package of applied programs, it is found that narrow and high street canyons are the least ventilated at a low wind velocity (~1 m/s), and the higher the street canyon with a constant width the higher the average concentration in the breathing zone. When studying the influence of the degree of heating of the surfaces of a street canyon with the same height and width, the least ventilated case is when the surface temperature of the windward vertical side of the canyon is 15–20°C higher than the ambient temperature. The main reason for this is the formation of a secondary vortex above the road surface, due to which the admixture is poorly carried out of the canyon.