FINITE ELEMENT SIMULATION OF NON-ISOTHERMAL POLLUTANT DISPERSION IN URBAN STREET CANYONS USING SHARED MEMORY PARALLELIZATION

Abstract

A finite element model to simulate pollutant dispersion and thermal effects over the flow field of urban street canyons is presented in this work. Street canyons constitute the basic geometric unit in urban areas, where a narrow passage surrounded by buildings is usually formed. In the street canyons, micro-scale meteorological processes dominate, which are mainly characterized by solar radiation effects and wind-induced flow patterns. Owing to the large amount of pollution emitted from engines of motor vehicles and geometrical configura- tions of the street canyons, air quality is considerably deteriorated in large cities, having an important impact on human health. In order to evaluate the pollutant dispersion in those ar- eas, field measurements, wind tunnel techniques and numerical simulation have been usually adopted. However, only numerical simulation can efficiently provide results with high spa- tial/temporal resolution and comprehensive information on the flow field and the pollutant transport. Therefore, a numerical model based on CFD techniques is proposed in this work to simulate incompressible flows considering heat and mass transfer phenomena. In the present model, an explicit two-step Taylor-Galerkin scheme is adopted where the spatial discretiza- tion is performed using the finite element method (FEM) with eight-node hexahedral ele- ments, one-point quadrature and hourglass control techniques. The pressure field is explicitly obtained by using the pseudo-compressibility hypothesis and the velocity and temperature fields are coupled by buoyancy forces according to the Boussinesq approximation. Large ed- dy simulation (LES) is utilized to analyze turbulent flows, where the sub-grid scales are mod- eled using both, the classical Smagorinsky's model and the dynamic model. Programming techniques for shared memory parallelization are also utilized in order to improve the per- formance of the present numerical code. Applications reproducing street-canyon configura- tions are numerically analyzed using a parametric study based on the main parameters util- ized to define the flow characteristics.