Street Pollution between Buildings

Pollution of the Street between Buildings — ANSYS Fluent CFD Simulation

Description

Motor vehicles are a significant source of air pollution, producing carbon dioxide, carbon monoxide, hydrocarbons, nitrogen oxides, particulate matter, and a range of mobile-source air toxics. The health risks associated with living close to roads are linked less to PM2.5 mass — only slightly elevated near roads — than to pollutants such as ultrafine particles, carbon monoxide, NO₂, black carbon, and polycyclic aromatic hydrocarbons, which are markedly higher near traffic. This project uses ANSYS Fluent to simulate pollution in a street placed between two buildings. Within the Urban Microclimate: All Levels CFD Training Package, this project extends pollutant dispersion to a realistic street configuration with buildings of differing size, building on the idealized canyon toward more representative urban layouts.

Methodology

The geometry is a 3D rectangular domain measuring 40 m × 20 m × 25 m in the X, Y, and Z directions, containing two buildings: the first 3 m × 3 m × 15 m and the second 3 m × 10 m × 15 m in the X, Y, and Z directions. The geometry is created in Design Modeler, and ANSYS Meshing generates 274,496 structured elements. The simulation is steady and uses a pressure-based solver, appropriate for the incompressible working fluid, with gravitational acceleration included at 9.81 m/s² in the negative Y direction. The Species Transport model is used to solve for the pollution rising from the street.

Analysis

At the end of the solution, two-dimensional contours of pressure, velocity, and the volume fractions of pollution and air are obtained, with the contours viewable at intervals through the solution. The static pressure is high on the left (windward) side of the buildings, while the velocity rises as the flow passes over their tops; the pollutant volume fraction tends toward the left building side, carried by the airflow moving between the buildings. The average static pressure at the inlet is plotted as a convergence criterion. By the end of this project, you'll be able to set up a steady Species Transport simulation of traffic pollution between buildings, account for gravity in the dispersion, and interpret the pressure, velocity, and pollutant-fraction fields around a real street configuration.