Preliminary study on the spread of air-borne pollutants in urban environment: a CFD simulation approach

The spreading of pollutants within urban areas, particularly from traffic emissions, poses a significant health risk. Computational Fluid Dynamics (CFD) has emerged as a key tool in understanding how pollutants spread within a city. In particular, the large-eddy simulation (LES) approach allows us to capture the complex time-dependent behaviour of the 3D flow field due to buildings in a dense urban environment. This work utilizes the CFD tool MGLET (Multi Grid Large Eddy Turbulence) to model the transport of pollutants within a selected domain in Munich city. MGLET offers a feature of simulating transport of multiple passive scalar quantities simultaneously. This facilitates the individual analysis of emissions from each major street in the domain of interest, providing detailed insights into their respective impacts. Additionally, MGLET utilizes the Immersed Boundary Method to resolve 3D building geometries, removing the need to generate body-fitted grids, which tends to be highly time-consuming. The streets are defined by area sources, and the emission rates for each street are defined by the average traffic flow rate. This high-fidelity approach offers a detailed analysis, allowing us to identify local features such as recirculation zones in street canyons and pinpoint the streets that contribute most significantly to pollution at specific locations. The insights from CFD studies can empower policymakers to craft legislation tailored to local pollution control efforts, thus enhancing the quality of life in urban areas. Ultimately, the accurate prediction of pollutant concentration is critical, as it directly impacts the health and well-being of urban residents, highlighting the urgent need for effective pollution control measures.