Numerical simulation of the distribution of vehicle emissions in a street canyon

The results of mathematical modeling of non-isothermal turbulent air flow and admixture transport in an idealized street canyon are presented. The simulation was based on the RANS model developed by the authors, the numerical algorithm, and the application package, which were improved to take into account the effect of the buoyancy force on aerodynamics and admixture transport. The mathematical model includes Reynolds-averaged stationary three-dimensional Navier-Stokes equations, equations of heat transfer and impurity transfer. For closing, a k-eps turbulence model was chosen taking into account the buoyancy forces. The numerical algorithm uses the finite volume method, non-uniform structured grids, and the fictitious domain method. Approximation of the differential problem is performed using Van Leer's monotonized linear upwind scheme and piecewise linear interpolation for dependent quantities. The resulting grid equations were solved sequentially by the iterative method of Buleev N. I. The SIMPLE algorithm was used to match the velocity and pressure fields. Using the developed package of applied programs, it was found that the least ventilated at low wind velocity ($\sim$ 1 m/s) are narrow and high street canyons, 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, the height and width of which coincide, the least ventilated case is when the surface temperature of the windward vertical side of the canyon is 15–20$^\circ$ С 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.