CFD modeling of traffic tidal flow: Assessment of pollutant dispersion

Pollutant distribution remains poorly understood when traffic tidal flows (TTFs) happen. By conducting computational fluid dynamic (CFD) simulations, the research efforts first focus on how different-side traffic-produced flow and turbulence (TPFT) affect in-canyon airflow and corresponding pollutant dispersion. Second, the composite effects of non-uniform traffic emission and TPFT are investigated. Finally, the influences of TTFs while varying different street canyon geometry and approaching wind condition is explored.

The results demonstrate that the turbulent diffusion terms enhanced by the traffic movement contribute to the pollutant dispersion around traffic lanes. Besides, both-side TPFTs push leeward pollutants towards traffic flow “downstream” due to the unidirectional advection terms along the traffic direction. Simultaneously considering the non-uniform traffic emission and TPFT, either leeward- or windward-congested TTFs has a higher concentration at the pedestrian level close to the congested traffic lane. Besides, the TTF with windward congestion has a higher volume-average concentration of the whole street canyon. With varying building separation, street canyon aspect ratio, and incoming wind direction, the TTFs still result in a larger pollutant accumulation above the pedestrian level, which is nearby the congested traffic flow.