Ventilation and Pollutant Concentration for the Pedestrian Zone, the Near-Wall Zone, and the Canopy Layer at Urban Intersections

To gain further insight into the ventilation at urban street intersections, this study conducted 3D simulations of the ventilation at right- and oblique-angled intersections under eight wind directions by using the Reynolds-averaged Navier–Stokes (RANS) <inline-formula><math xmlns="htt...

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Autores principales:	Mingjie Zhang, Zhi Gao, Xin Guo, Jialei Shen
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	intersections typology CFD simulations pedestrian ventilation near-wall concentration volumetric flow rate age of air Medicine R
Acceso en línea:	https://doaj.org/article/7715d49853634fae87236b264c64c0c5
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spelling	oai:doaj.org-article:7715d49853634fae87236b264c64c0c52021-11-11T16:13:33ZVentilation and Pollutant Concentration for the Pedestrian Zone, the Near-Wall Zone, and the Canopy Layer at Urban Intersections10.3390/ijerph1821110801660-46011661-7827https://doaj.org/article/7715d49853634fae87236b264c64c0c52021-10-01T00:00:00Zhttps://www.mdpi.com/1660-4601/18/21/11080https://doaj.org/toc/1661-7827https://doaj.org/toc/1660-4601To gain further insight into the ventilation at urban street intersections, this study conducted 3D simulations of the ventilation at right- and oblique-angled intersections under eight wind directions by using the Reynolds-averaged Navier–Stokes (RANS) <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="sans-serif">κ</mi></semantics></math></inline-formula>-ε turbulence model. The divergent responses of ventilation and pollution concentration for the pedestrian zone (ped), the near-wall zone (nwz), and the canopy layer to the change in intersection typology and wind direction were investigated. The flow characteristics of the intersections, taken as the air flow hub, were explored by employing indices such as the minimum flow ratio (β) between horizontal openings. The results show that oblique wind directions lead to a lower total volumetric flow rate (Q<sub>total</sub>) but a higher β value for right-angled intersections. For T-shaped intersections, a larger cross-sectional area for the outflow helps to increase Q<sub>total</sub>. Oblique-angled intersections, for example, the X-shaped intersection, experience a more significant difference in Q<sub>total</sub> but a steady value of β when the wind direction changes. The vertical air-exchange rate for the intersection was particularly significant when the wind directions were parallel to the street orientation or when there was no opening in the inflow direction. The spatially averaged normalized pollutant concentration and age of air (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mrow><msup><mi mathvariant="sans-serif">τ</mi><mo></mo></msup></mrow><mo stretchy="true">¯</mo></mover></mrow></semantics></math></inline-formula>) for the pedestrian zone and the canopy layer showed similar changing trends for most of the cases, while in some cases, only the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mrow><msubsup><mi mathvariant="sans-serif">τ</mi><mrow><mi>ped</mi></mrow><mo></mo></msubsup></mrow><mo stretchy="true">¯</mo></mover></mrow></semantics></math></inline-formula> or <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mrow><msubsup><mi mathvariant="sans-serif">τ</mi><mrow><mi>nwz</mi></mrow><mo>*</mo></msubsup></mrow><mo stretchy="true">¯</mo></mover></mrow></semantics></math></inline-formula> changed obviously. These findings reveal the impact mechanism of intersection configuration on urban local ventilation and pollutant diffusion.Mingjie ZhangZhi GaoXin GuoJialei ShenMDPI AGarticleintersections typologyCFD simulationspedestrian ventilationnear-wall concentrationvolumetric flow rateage of airMedicineRENInternational Journal of Environmental Research and Public Health, Vol 18, Iss 11080, p 11080 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	intersections typology CFD simulations pedestrian ventilation near-wall concentration volumetric flow rate age of air Medicine R
spellingShingle	intersections typology CFD simulations pedestrian ventilation near-wall concentration volumetric flow rate age of air Medicine R Mingjie Zhang Zhi Gao Xin Guo Jialei Shen Ventilation and Pollutant Concentration for the Pedestrian Zone, the Near-Wall Zone, and the Canopy Layer at Urban Intersections
description	To gain further insight into the ventilation at urban street intersections, this study conducted 3D simulations of the ventilation at right- and oblique-angled intersections under eight wind directions by using the Reynolds-averaged Navier–Stokes (RANS) <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="sans-serif">κ</mi></semantics></math></inline-formula>-ε turbulence model. The divergent responses of ventilation and pollution concentration for the pedestrian zone (ped), the near-wall zone (nwz), and the canopy layer to the change in intersection typology and wind direction were investigated. The flow characteristics of the intersections, taken as the air flow hub, were explored by employing indices such as the minimum flow ratio (β) between horizontal openings. The results show that oblique wind directions lead to a lower total volumetric flow rate (Q<sub>total</sub>) but a higher β value for right-angled intersections. For T-shaped intersections, a larger cross-sectional area for the outflow helps to increase Q<sub>total</sub>. Oblique-angled intersections, for example, the X-shaped intersection, experience a more significant difference in Q<sub>total</sub> but a steady value of β when the wind direction changes. The vertical air-exchange rate for the intersection was particularly significant when the wind directions were parallel to the street orientation or when there was no opening in the inflow direction. The spatially averaged normalized pollutant concentration and age of air (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mrow><msup><mi mathvariant="sans-serif">τ</mi><mo></mo></msup></mrow><mo stretchy="true">¯</mo></mover></mrow></semantics></math></inline-formula>) for the pedestrian zone and the canopy layer showed similar changing trends for most of the cases, while in some cases, only the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mrow><msubsup><mi mathvariant="sans-serif">τ</mi><mrow><mi>ped</mi></mrow><mo></mo></msubsup></mrow><mo stretchy="true">¯</mo></mover></mrow></semantics></math></inline-formula> or <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mrow><msubsup><mi mathvariant="sans-serif">τ</mi><mrow><mi>nwz</mi></mrow><mo>*</mo></msubsup></mrow><mo stretchy="true">¯</mo></mover></mrow></semantics></math></inline-formula> changed obviously. These findings reveal the impact mechanism of intersection configuration on urban local ventilation and pollutant diffusion.
format	article
author	Mingjie Zhang Zhi Gao Xin Guo Jialei Shen
author_facet	Mingjie Zhang Zhi Gao Xin Guo Jialei Shen
author_sort	Mingjie Zhang
title	Ventilation and Pollutant Concentration for the Pedestrian Zone, the Near-Wall Zone, and the Canopy Layer at Urban Intersections
title_short	Ventilation and Pollutant Concentration for the Pedestrian Zone, the Near-Wall Zone, and the Canopy Layer at Urban Intersections
title_full	Ventilation and Pollutant Concentration for the Pedestrian Zone, the Near-Wall Zone, and the Canopy Layer at Urban Intersections
title_fullStr	Ventilation and Pollutant Concentration for the Pedestrian Zone, the Near-Wall Zone, and the Canopy Layer at Urban Intersections
title_full_unstemmed	Ventilation and Pollutant Concentration for the Pedestrian Zone, the Near-Wall Zone, and the Canopy Layer at Urban Intersections
title_sort	ventilation and pollutant concentration for the pedestrian zone, the near-wall zone, and the canopy layer at urban intersections
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/7715d49853634fae87236b264c64c0c5
work_keys_str_mv	AT mingjiezhang ventilationandpollutantconcentrationforthepedestrianzonethenearwallzoneandthecanopylayeraturbanintersections AT zhigao ventilationandpollutantconcentrationforthepedestrianzonethenearwallzoneandthecanopylayeraturbanintersections AT xinguo ventilationandpollutantconcentrationforthepedestrianzonethenearwallzoneandthecanopylayeraturbanintersections AT jialeishen ventilationandpollutantconcentrationforthepedestrianzonethenearwallzoneandthecanopylayeraturbanintersections
_version_	1718432364248432640

Ventilation and Pollutant Concentration for the Pedestrian Zone, the Near-Wall Zone, and the Canopy Layer at Urban Intersections

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