A Numerical Model for Pullatant Dispersion Simulation in Street Canyons

Abstract

In this work, pollutant dispersion analyses in urban areas are carried out employing a model developed for numerical simulation of incompressible flows considering the effects of heat and mass transfer. Air pollution generated by vehicles with internal combustion engines is one of the biggest problems the large cities are facing today. Therefore, the development of numerical techniques for evaluating and controlling the levels of pollutants is essential to maintain the urban environment balance. In the central regions of large cities, the so-called street canyons represent the basic geometric unit, where significant changes can be observed in the wind flow and pollutant dispersion as function of thermal conditions and the geometrical configuration of the canyons. In the present model, an explicit two-step Taylor-Galerkin scheme is adopted where the spatial discretization is performed using the finite element method (FEM) with eight-node hexahedral elements, one-point quadrature and hourglass control techniques. The pressure field is explicitly obtained by using the pseudocompressibility hypothesis and the velocity and temperature fields are coupled by buoyancy forces according to the Boussinesq approximation. Large eddy simulation (LES) is utilized to analyze turbulent flows, where the sub-grid scales are modeled using both, the classical Smagorinsky`s model and the dynamic model. Applications involving isothermal and non-isothermal flows are reproduced in order to validate the numerical model presented here and isothermal pollutant dispersion problems are simulated considering different geometrical configurations represented by two and three-dimensional models in order to adequately characterize the conditions encountered in urban areas.