Pollution in a Real Urban Zone

Pollution in a Real Urban Zone — ANSYS Fluent CFD Simulation

Description

Urban environments are the most important context of daily life, and in many developing countries air-quality conditions worsen year on year, even as technology reduces per-vehicle emissions — because transportation demand keeps rising. This project uses ANSYS Fluent to calculate how carbon dioxide from car exhaust is dispersed across an urban zone, using the Species Transport model to solve a transport equation for each component of the pollutant mixture. The purpose is to investigate the effect of free airflow on the CO₂ produced by traffic within a real city-street setting. Within the Urban Microclimate: All Levels CFD Training Package, this project scales pollutant dispersion up to an urban complex of multiple building blocks, representing the district-scale air-quality problem.

Methodology

The three-dimensional model is drawn in Design Modeler as a set of structural elements — several building blocks and a street belonging to a city — enclosed within a rectangular domain of 9 m × 13 m × 4 m around the urban complex. The airflow inlet is selected on three lateral faces of the domain, and a 0.1 m high area on one of the city streets acts as the CO₂ source, with a carbon-dioxide production rate of 4 kg/m³. Meshing in ANSYS Meshing is unstructured with 4,137,570 elements, refined near the internal boundaries for higher accuracy. Because both air and CO₂ are modeled, the Species Transport model is used, and the solver is pressure-based. The simulation is transient, since the goal is to study how the CO₂ concentration changes over time. Free airflow enters at 0.2 m/s and 300 K with zero CO₂ mass fraction; the outlet is a pressure outlet at 0 Pa gauge; and the walls are stationary with zero heat flux. Turbulence uses the standard k-epsilon model with standard wall functions, the energy equation is on, pressure–velocity coupling uses SIMPLE, and the solution is initialized with the standard method.

Analysis

At the end of the solution, two-dimensional contours of pressure, temperature, velocity, and air and CO₂ mass fraction are obtained across the whole model in the XY and YZ sections, along with three-dimensional contours of the same quantities in the region of the CO₂ source. These fields show how the free airflow transports and dilutes the emitted CO₂ across the urban zone and around the surrounding building blocks. The project includes the geometry and mesh file and a comprehensive training movie demonstrating the full solution and result extraction. By the end of this project, you'll be able to set up a transient Species Transport simulation on an urban complex, define a street-level CO₂ source, and interpret the concentration fields that reveal how effectively an urban zone ventilates traffic emissions.