The model of transfer of atmosphere pollution in roadside vegetation near the highway

Abstract

The work is devoted to the development of a model and investigation of the process of pollution transfer in the ground layer of a general-purpose motor road with plantations and terrain. As the basis of the model, a long section of a road with a roadside terrain and plantings is considered. Along the axial line of the road, a linear source is assumed, which releases constant impurity consumption along the road. The impurity is transported in the surface layer of the highway in the conditions of the lateral wind curve, alternating relief of the adjacent terrain and roadside plantations of different densities. The model is based on a grid description of the three-dimensional region under consideration. The motion of air continuous medium is described by the Reynolds averaged Navier-Stokes equations. The air continuous medium is assumed to be incompressible, multicomponent, and chemically nonreactive. To model the turbulent transport effects, two-parameter differential turbulence model with wall functions is used as the basis. Simulation of blocking of leaf space and tree branches is performed on the basis of blocking with a porous medium. The Navier-Stokes equations, as well as transport equations for the parameters of the turbulence model, contain source terms in the right-hand parts in the form of a power-law dependence of the velocity modulus in the porosity regions. This model interprets the influence of vegetation as a homogeneous isotropic resistance of a low-inertial volume; the additional terms in the equations of the turbulence model increase the production of turbulence. The study was carried out using the author's software package MTFS®, in which the basic implicit algorithm is provided by the method of variable directions and TVD scheme of 2/3-th order accuracy. The calculations were performed by the method of establishing the flow from a retarded state to a developed steady-state flow in the middle. The flow outside the calculated region was assumed to be completely turbulent, which was determined by the input boundary conditions. The input wind speed profile was used with allowance for the boundary layer. Simulation of impurity distribution for a long rectilinear section was performed and a satisfactory agreement with experimental data was obtained. A study was carried out in areas with a substantially spatial impurity transport structure. It is shown that the slope of the current lines with respect to the axial line of the road facilitates the demolition of the impurity along the road, while the intensity of the vorticity between the plantations decreases in comparison with the two-dimensional model.Кey words: highway; roadside vegetation; boundary layer; transfer of pollutants.