Impacts of shape and height of upstream roof on airflow and pollutant dispersion inside an urban street canyon

Abstract

A two-dimensional numerical model for simulating flow and pollutant dispersion in an urban street canyon is firstly developed using the FLUENT code and then validated against the wind tunnel results. After this, the flow field and pollutant dispersion inside an urban street canyon with aspect ratio W/H = 1 are examined numerically considering five different shapes (vaulted, trapezoidal, slanted, upward wedged, and downward wedged roofs) as well as three different roof height to building height ratios (Z H /H = 1/6, 1/3, and 1/2) for the upstream building roof. The results obtained reveal that the shape and height of an upstream roof have significant influences on flow pattern and pollutant distribution in an urban canyon. A large single clockwise vortex is generated in the canyon for the vaulted upstream roof at Z H /H = 1/6, 1/3, and 1/2, the trapezoidal and downward wedged roofs at Z H /H = 1/6 and 1/3, and the slanted and upward wedged roofs at Z H /H = 1/6, while a main clockwise vortex and a secondary counterclockwise vortex are established for the trapezoidal and downward wedged roofs at Z H /H = 1/2 and the slanted and upward wedged roofs at Z H /H = 1/3 and 1/2. In the one-vortex flow regime, the clockwise vortex moves upward and grows in size with increasing upstream roof height for the vaulted, trapezoidal, and downward wedged roofs. In the two-vortex flow regime, the size and rotational velocity of both upper clockwise and lower counterclockwise vortices increase with the upstream roof height for the slanted and upward wedged roofs. At Z H /H = 1/6, the pollution levels in the canyon are close among all the upstream roof shapes studied. At Z H /H = 1/3, the pollution levels in the canyon for the upward wedged roof and slanted roof are much higher than those for the vaulted, trapezoidal, and downward wedged roofs. At Z H /H = 1/2, the lowest pollution level appears in the canyon for the vaulted upstream roof, while the highest pollution level occurs in the canyon for the upward wedged roof.

Modeling the Airflow and Particle Dispersion in Street Canyons under Unsteady Thermal Environment with Sinusoidal Variation

“…A two-dimensional (2D) street canyon is a simplification of an actual urban geometry. Numerous studies have focused on the impact of building characteristics (such as building heights, the shape roof of building, and the density of the building group) on the diffusion of pollutants in idealized and modeling urban street canyons (Li et al, 2008;Huang et al, 2009;Li et al, 2010;Buccolieri et al, 2011;Scargiali et al, 2011;Hang et al, 2012;Addepalli and Pardyjak, 2013;Scungio, 2013;Huang et al, 2015). Scungio et al (2015a) have used the detached eddy simulation to study the turbulent flow in isolated street canyons of different aspect ratios.…”

Effects of the Horizontal Elements on Windward Wall of Buildings on Natural Ventilation and Pollutant Dispersion

“…According to Huang et al [5] and Wang et al [9], the wind in both outdoor and indoor environments is numerically stable and could be regarded as incompressible turbulent flow. To simplify the simulation, the buoyancy effects due to solar radiation was not considered in this study.…”

“…building height and the street width. Takano et al [4] and Huang et al [5] found that the shape of roof may influent the pollutant concentration inside the street canyon. Besides, a lot of investigators took attention to the indoor ventilation coupling with air flow in the urban street canyon.…”

The influence of wind speed on airflow and fine particle transport within different building layouts of an industrial city

“…CONTACT Numerous studies have qualitatively focused on the impacts of building heights (Li, Liu, and Leung 2008), shape of building roofs (Huang, Hu, and Zeng 2009), and density of building groups (Scargiali et al 2011) on the diffusion of pollutants (Addepalli and Pardyjak 2013;Gu et al 2011;Hang et al 2012;Huang, He, and Kim 2015;Scungio 2013). Hang et al (2012) numerically studied a parallel approaching wind on arrays of uniform height, using a normalized pollutant transport rate to quantify the contribution of mean flow and turbulent diffusion to pollutant removal.…”