Three-dimensional modeling of air flow and pollutant dispersion in an urban street canyon with thermal effects.
Effects of excess ground and building temperatures on airflow and dispersion of pollutants in an urban street canyon with an aspect ratio of 0.8 and a length-to-width ratio of 3 were investigated numerically. Three-dimensional governing equations of mass, momentum, energy, and species were modeled using the RNG k-epsilon turbulence model and Boussinesq approximation, which were solved using the finite volume method. Vehicle emissions were estimated from the measured traffic flow rates and modeled as banded line sources, with a street length and bandwidths equal to typical vehicle widths. Both measurements and simulations reveal that pollutant concentrations typically follow the traffic flow rate; they decline as the height increases and are higher on the leeward side than on the windward side. Three-dimensional simulations reveal that the vortex line, joining the centers of cross-sectional vortexes of the street canyon, meanders between street buildings and shifts toward the windward side when heating strength is increased. Thermal boundary layers are very thin. Entrainment of outside air increases, and pollutant concentration decreases with increasing heating condition. Also, traffic-produced turbulence enhances the turbulent kinetic energy and the mixing of temperature and admixtures in the canyon. Factors affecting the inaccuracy of the simulations are addressed.
Tsai
Mong-Yu
MY
Institute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan, Republic of China.
Chen
Kang-Shin
KS
Wu
Chung-Hsing
CH
D000392:Air Movements; D000393:Air Pollutants / Q000032:analysis*; D002248:Carbon Monoxide / Q000032:analysis; D002947:Cities; D003198:Computer Simulation; D004784:Environmental Monitoring; D005160:Facility Design and Construction; D008962:Models, Theoretical; D018986:Motor Vehicles; D009589:Nitrogen Oxides / Q000032:analysis; D013458:Sulfur Dioxide / Q000032:analysis; D013624:Taiwan; D013696:Temperature; D014919:Wind
D000393:Air Pollutants; D009589:Nitrogen Oxides; D013458:Sulfur Dioxide; D002248:Carbon Monoxide