Urban pollution and indoor air quality, an undisputed relationship: CFD modelling of single-sided pollutant ingress

This study simulates near-field pollutant dispersion and subsequent ingress into building envelopes within urban street canyons via computational fluid dynamics (CFD). Qualitative pollutant dispersal experiments conducted in wind tunnels are compared against numerical simulation. Two street-canyon aspect ratios were investigated (Height/Width=0.5 & 1). Roof angles were investigated (flat and 26.6º). An open window was located on the on the leeward side connecting to an interior room. ANSYS Fluent 15 was used to model airflow and employed a k-omega turbulence model. CO2 tracer was released between the buildings and concentrations were measured inside the open window. Increasing canyon width reduced the residence time of pollutant and reduces ingress. Flat roofs for both ratios drew CO2 to the leeward side of the building due to negative pressures. However pitched roofs created more complex systems that reduced contaminant in the canyon due to unsteady vortices. This may indicate a decrease in vertical exchange due to intermittent turbulent structures which maintain overall mass transfer with the air above.