BIOM&S Seminar: Numerical Simulation of Wind Flow and Pollutant Dispersion in Urban Street Canyons

SPEAKER:   Van Thinh Nguyen

Department of Civil and Environmental Engineering, Seoul National University, South Korea

ABSTRACT: 

Pollution from industrial activities, vehicle exhaust, heating and cooling systems, etc. can cause fatal harms to humans in urban street canyons, therefore investigation of flow characteristics and pollution transports in street canyons is a crucial task in the urban environment. The most important characteristics of the flow in street canyons are the wind-induced flow patterns characterizing by internal flow, flow separation and reattachment, which effect on the local air quality and consequently on the human health in urban areas. For such flows it is very difficult to accurately calculate flow patterns and pollutant transports. The study on wind flow and pollutant transport inside and over urban street canyons have attracted great concern during last three decades due to the speedy urbanization and city enlargement. Field measurements and laboratory-scale physical modeling are not only very expensive but also difficult, and somehow impossible due to the temporal and spatial scales and complex geometries of urban street canyons. Advantage from the increasing of computer technology (HPC facility), numerical model becomes the most practical and powerful tool for the simulation of wind flows and pollutant transport in urban street canyons.

In this study, we have developed a numerical model based on an open source CFD package OpenFOAM to study the flow pattern and pollutant transport in urban street canyons.  In the new model, the scalar transport equation for pollutants is coupled with momentum equation of airflow by RANS (Reynolds Averaged Navier-Stokes) equations using various two-equation turbulence closure models. The numerical model has been calibrated and validated against different well-known laboratory experiments, then applied to various street canyon geometries with different aspect ratios (relationship between the height of building and the width of street canyon) and roof shapes (flat, shed, gable, and round). The comparisons between the simulations and observations show a good agreement on the flow patterns and pollutant transports. As a result, the new model can be applied to the simulation of the wind flow and pollutant dispersion in urban street canyons.  

Keywords: Street canyons, roof shape, aspect ratio, numerical simulation, turbulent flow, pollution transport.