Street-canyon pollution with respect to urban-array complexity: The role of lateral and mean pollution fluxes

• Published in: Building and environment 2018-06, Vol.138, p.221-234
• Main Authors: Nosek, Štěpán, Fuka, Vladimír, Kukačka, Libor, Kluková, Zuzana, Jaňour, Zbyněk
• Format: Article
• Language: English
• Subjects: Canyons; Complexity; Computational modelling; Entrainment; Fluid dynamics; Fluxes; Large eddy simulation; Nonuniformity; Outdoor air quality; Pitched roofs; Pollutant removal; Pollutants; Pollution; Pollution dispersion; Pollution flux; Roads & highways; Street canyon; Street canyons; Urban air quality; Urban areas; Urban environments; Ventilation; Wind measurement; Wind tunnels; Wind-tunnel experiment
• ISSN: 0360-1323; 1873-684X
• DOI: 10.1016/j.buildenv.2018.04.036

The prediction of pollution within street canyons remains challenging due to the complexity of turbulent flows in urban environments. To improve our understanding of these flows and their relation to the ventilation of street-canyons, we studied pollution fluxes through all street-canyon openings and their balance with respect to urban-array complexity using large-eddy simulations (LES). We validated the LES with wind-tunnel measurements using mean velocities and concentrations and the mean total and turbulent pollution fluxes at the top and lateral openings of the street canyons with either uniform or nonuniform heights and pitched roofs. The LES confirm and extend recent findings about the importance of mean horizontal pollution fluxes for pollutant transport within a street network. The mean fluxes have at least the same dominance as the turbulent ones in case of lateral openings. In case of top openings, the mean fluxes clearly dominate if openings at the roof eaves are selected. While pollutant removal and entrainment through lateral openings are negligible in case of uniform canyons, they are notable in case of nonuniform canyons. We demonstrate that urban roof height nonuniformity does not necessarily enhance the street-canyon ventilation because it worsens (by a factor of 1.1) or improves (by a factor of 1.5) the ventilation compared with the urban uniform height. •LES validated with measured turbulent and mean pollution fluxes.•Mean flow governs the street-canyon ventilation at eaves of pitched roofs.•Roof height non-uniformity increases the lateral mean pollution fluxes.•The roof height non-uniformity improves or worsens the street-canyon ventilation.