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Article: Passive urban ventilation by combined buoyancy-driven slope flow and wall flow: parametric CFD studies on idealized city models
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TitlePassive urban ventilation by combined buoyancy-driven slope flow and wall flow: parametric CFD studies on idealized city models
 
AuthorsLuo, Z1
Li, Y1
 
KeywordsAge of air
Air change rates
Background winds
Building height
Buoyancy driven flows
 
Issue Date2011
 
PublisherPergamon. The Journal's web site is located at http://www.elsevier.com/locate/atmosenv
 
CitationAtmospheric Environment, 2011, v. 45 n. 32, p. 5946-5956 [How to Cite?]
DOI: http://dx.doi.org/10.1016/j.atmosenv.2011.04.010
 
AbstractThis paper reports the results of a parametric CFD study on idealized city models to investigate the potential of slope flow in ventilating a city located in a mountainous region when the background synoptic wind is absent. Examples of such a city include Tokyo in Japan, Los Angeles and Phoenix in the US, and Hong Kong. Two types of buoyancy-driven flow are considered, i.e., slope flow from the mountain slope (katabatic wind at night and anabatic wind in the daytime), and wall flow due to heated/cooled urban surfaces. The combined buoyancy-driven flow system can serve the purpose of dispersing the accumulated urban air pollutants when the background wind is weak or absent. The microscopic picture of ventilation performance within the urban structures was evaluated in terms of air change rate (ACH) and age of air. The simulation results reveal that the slope flow plays an important role in ventilating the urban area, especially in calm conditions. Katabatic flow at night is conducive to mitigating the nocturnal urban heat island. In the present parametric study, the mountain slope angle and mountain height are assumed to be constant, and the changing variables are heating/cooling intensity and building height. For a typical mountain of 500 m inclined at an angle of 20° to the horizontal level, the interactive structure is very much dependent on the ratio of heating/cooling intensity as well as building height. When the building is lower than 60 m, the slope wind dominates. When the building is as high as 100 m, the contribution from the urban wall flow cannot be ignored. It is found that katabatic wind can be very beneficial to the thermal environment as well as air quality at the pedestrian level. The air change rate for the pedestrian volume can be as high as 300 ACH. © 2011 Elsevier Ltd.
 
ISSN1352-2310
2013 Impact Factor: 3.062
2013 SCImago Journal Rankings: 1.776
 
DOIhttp://dx.doi.org/10.1016/j.atmosenv.2011.04.010
 
ISI Accession Number IDWOS:000295607300032
Funding AgencyGrant Number
Research Grants Council of Hong Kong Special Administrative Region, ChinaHKU 7145/07E
Funding Information:

The work described was supported by the Research Grants Council of Hong Kong Special Administrative Region, China (Project No. HKU 7145/07E). We thank two anonymous reviewers' comments to further improve the paper.

 
ReferencesReferences in Scopus
 
DC FieldValue
dc.contributor.authorLuo, Z
 
dc.contributor.authorLi, Y
 
dc.date.accessioned2012-08-08T08:45:34Z
 
dc.date.available2012-08-08T08:45:34Z
 
dc.date.issued2011
 
dc.description.abstractThis paper reports the results of a parametric CFD study on idealized city models to investigate the potential of slope flow in ventilating a city located in a mountainous region when the background synoptic wind is absent. Examples of such a city include Tokyo in Japan, Los Angeles and Phoenix in the US, and Hong Kong. Two types of buoyancy-driven flow are considered, i.e., slope flow from the mountain slope (katabatic wind at night and anabatic wind in the daytime), and wall flow due to heated/cooled urban surfaces. The combined buoyancy-driven flow system can serve the purpose of dispersing the accumulated urban air pollutants when the background wind is weak or absent. The microscopic picture of ventilation performance within the urban structures was evaluated in terms of air change rate (ACH) and age of air. The simulation results reveal that the slope flow plays an important role in ventilating the urban area, especially in calm conditions. Katabatic flow at night is conducive to mitigating the nocturnal urban heat island. In the present parametric study, the mountain slope angle and mountain height are assumed to be constant, and the changing variables are heating/cooling intensity and building height. For a typical mountain of 500 m inclined at an angle of 20° to the horizontal level, the interactive structure is very much dependent on the ratio of heating/cooling intensity as well as building height. When the building is lower than 60 m, the slope wind dominates. When the building is as high as 100 m, the contribution from the urban wall flow cannot be ignored. It is found that katabatic wind can be very beneficial to the thermal environment as well as air quality at the pedestrian level. The air change rate for the pedestrian volume can be as high as 300 ACH. © 2011 Elsevier Ltd.
 
dc.description.natureLink_to_subscribed_fulltext
 
dc.identifier.citationAtmospheric Environment, 2011, v. 45 n. 32, p. 5946-5956 [How to Cite?]
DOI: http://dx.doi.org/10.1016/j.atmosenv.2011.04.010
 
dc.identifier.doihttp://dx.doi.org/10.1016/j.atmosenv.2011.04.010
 
dc.identifier.epage5956
 
dc.identifier.hkuros209897
 
dc.identifier.isiWOS:000295607300032
Funding AgencyGrant Number
Research Grants Council of Hong Kong Special Administrative Region, ChinaHKU 7145/07E
Funding Information:

The work described was supported by the Research Grants Council of Hong Kong Special Administrative Region, China (Project No. HKU 7145/07E). We thank two anonymous reviewers' comments to further improve the paper.

 
dc.identifier.issn1352-2310
2013 Impact Factor: 3.062
2013 SCImago Journal Rankings: 1.776
 
dc.identifier.issue32
 
dc.identifier.scopuseid_2-s2.0-81155162506
 
dc.identifier.spage5946
 
dc.identifier.urihttp://hdl.handle.net/10722/157155
 
dc.identifier.volume45
 
dc.languageeng
 
dc.publisherPergamon. The Journal's web site is located at http://www.elsevier.com/locate/atmosenv
 
dc.publisher.placeUnited Kingdom
 
dc.relation.ispartofAtmospheric Environment
 
dc.relation.referencesReferences in Scopus
 
dc.subjectAge of air
 
dc.subjectAir change rates
 
dc.subjectBackground winds
 
dc.subjectBuilding height
 
dc.subjectBuoyancy driven flows
 
dc.titlePassive urban ventilation by combined buoyancy-driven slope flow and wall flow: parametric CFD studies on idealized city models
 
dc.typeArticle
 
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<description.abstract>This paper reports the results of a parametric CFD study on idealized city models to investigate the potential of slope flow in ventilating a city located in a mountainous region when the background synoptic wind is absent. Examples of such a city include Tokyo in Japan, Los Angeles and Phoenix in the US, and Hong Kong. Two types of buoyancy-driven flow are considered, i.e., slope flow from the mountain slope (katabatic wind at night and anabatic wind in the daytime), and wall flow due to heated/cooled urban surfaces. The combined buoyancy-driven flow system can serve the purpose of dispersing the accumulated urban air pollutants when the background wind is weak or absent. The microscopic picture of ventilation performance within the urban structures was evaluated in terms of air change rate (ACH) and age of air. The simulation results reveal that the slope flow plays an important role in ventilating the urban area, especially in calm conditions. Katabatic flow at night is conducive to mitigating the nocturnal urban heat island. In the present parametric study, the mountain slope angle and mountain height are assumed to be constant, and the changing variables are heating/cooling intensity and building height. For a typical mountain of 500 m inclined at an angle of 20&#176; to the horizontal level, the interactive structure is very much dependent on the ratio of heating/cooling intensity as well as building height. When the building is lower than 60 m, the slope wind dominates. When the building is as high as 100 m, the contribution from the urban wall flow cannot be ignored. It is found that katabatic wind can be very beneficial to the thermal environment as well as air quality at the pedestrian level. The air change rate for the pedestrian volume can be as high as 300 ACH. &#169; 2011 Elsevier Ltd.</description.abstract>
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Author Affiliations
  1. The University of Hong Kong