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Article: On the contribution of mean flow and turbulence to city breathability: the case of long streets with tall buildings
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TitleOn the contribution of mean flow and turbulence to city breathability: the case of long streets with tall buildings
 
AuthorsHang, J1 4
Li, Y1
Buccolieri, R3
Sandberg, M2
Di Sabatino, S3
 
Issue Date2012
 
PublisherElsevier BV. The Journal's web site is located at http://www.elsevier.com/locate/scitotenv
 
CitationScience of the Total Environment, 2012, v. 416, p. 362-373 [How to Cite?]
DOI: http://dx.doi.org/10.1016/j.scitotenv.2011.12.016
 
AbstractThis paper analyses the contribution of mean flow and turbulence to city breathability within urban canopy layers under the hypothesis that winds from rural/marine areas are sources of clean air (inhale effect) and main contributors to local-scale pollutant dilution (exhale effect). Using Computational Fluid Dynamics (CFD) simulations, several idealized long streets flanked by tall buildings are investigated for wind flow parallel to the street axis. Aspect ratios (building height/street width) ranging from 2 to 4 and street lengths ranging from neighborhood scales (1km in full scale) to city scales (10km in full scale) are analyzed. To assess the inhale effect, the age of air concept is applied to quantify the time taken by a parcel of rural/marine air to reach a reference location within the urban canopy layer. To simulate the exhale effect, removal of pollutants released from a ground level source is considered. Numerical results agree with wind tunnel observations showing that a bulk portion of rural/marine air enters the streets through windward entries, a smaller part of it leaves through street roofs and the remaining fraction blows through the street aiding pollutant dilution. Substantial differences between neighborhood-scale and city-scale configurations are found. For neighborhood-scale models, pollutant removal by rural/marine air is mainly associated to mean flow along the streets. Breathability improves in streets flanked by taller buildings since in this case more rural/marine air is captured inside canyons leading to stronger wind along the street. For city-scale models, pollutant removal due to turbulent fluctuations across street roofs competes with that due to mean flows along the street. Breathability improves in streets flanked by lower buildings in which less rural/marine air is driven out and pollutant removal by turbulent fluctuations is more effective. Based on these findings, suggestions for ventilation strategies for urban areas with tall buildings are provided.
 
ISSN0048-9697
2013 Impact Factor: 3.163
2013 SCImago Journal Rankings: 1.530
 
DOIhttp://dx.doi.org/10.1016/j.scitotenv.2011.12.016
 
ISI Accession Number IDWOS:000301155200041
Funding AgencyGrant Number
University of Hong Kong on Initiative of Clean Energy for Environment
Funding Information:

The present work in this paper is supported by a University Development Fund from the University of Hong Kong on Initiative of Clean Energy for Environment.

 
ReferencesReferences in Scopus
 
DC FieldValue
dc.contributor.authorHang, J
 
dc.contributor.authorLi, Y
 
dc.contributor.authorBuccolieri, R
 
dc.contributor.authorSandberg, M
 
dc.contributor.authorDi Sabatino, S
 
dc.date.accessioned2012-08-08T08:45:38Z
 
dc.date.available2012-08-08T08:45:38Z
 
dc.date.issued2012
 
dc.description.abstractThis paper analyses the contribution of mean flow and turbulence to city breathability within urban canopy layers under the hypothesis that winds from rural/marine areas are sources of clean air (inhale effect) and main contributors to local-scale pollutant dilution (exhale effect). Using Computational Fluid Dynamics (CFD) simulations, several idealized long streets flanked by tall buildings are investigated for wind flow parallel to the street axis. Aspect ratios (building height/street width) ranging from 2 to 4 and street lengths ranging from neighborhood scales (1km in full scale) to city scales (10km in full scale) are analyzed. To assess the inhale effect, the age of air concept is applied to quantify the time taken by a parcel of rural/marine air to reach a reference location within the urban canopy layer. To simulate the exhale effect, removal of pollutants released from a ground level source is considered. Numerical results agree with wind tunnel observations showing that a bulk portion of rural/marine air enters the streets through windward entries, a smaller part of it leaves through street roofs and the remaining fraction blows through the street aiding pollutant dilution. Substantial differences between neighborhood-scale and city-scale configurations are found. For neighborhood-scale models, pollutant removal by rural/marine air is mainly associated to mean flow along the streets. Breathability improves in streets flanked by taller buildings since in this case more rural/marine air is captured inside canyons leading to stronger wind along the street. For city-scale models, pollutant removal due to turbulent fluctuations across street roofs competes with that due to mean flows along the street. Breathability improves in streets flanked by lower buildings in which less rural/marine air is driven out and pollutant removal by turbulent fluctuations is more effective. Based on these findings, suggestions for ventilation strategies for urban areas with tall buildings are provided.
 
dc.description.natureLink_to_subscribed_fulltext
 
dc.identifier.citationScience of the Total Environment, 2012, v. 416, p. 362-373 [How to Cite?]
DOI: http://dx.doi.org/10.1016/j.scitotenv.2011.12.016
 
dc.identifier.citeulike10233888
 
dc.identifier.doihttp://dx.doi.org/10.1016/j.scitotenv.2011.12.016
 
dc.identifier.epage373
 
dc.identifier.hkuros205319
 
dc.identifier.isiWOS:000301155200041
Funding AgencyGrant Number
University of Hong Kong on Initiative of Clean Energy for Environment
Funding Information:

The present work in this paper is supported by a University Development Fund from the University of Hong Kong on Initiative of Clean Energy for Environment.

 
dc.identifier.issn0048-9697
2013 Impact Factor: 3.163
2013 SCImago Journal Rankings: 1.530
 
dc.identifier.pmid22226399
 
dc.identifier.scopuseid_2-s2.0-84856226321
 
dc.identifier.spage362
 
dc.identifier.urihttp://hdl.handle.net/10722/157171
 
dc.identifier.volume416
 
dc.languageeng
 
dc.publisherElsevier BV. The Journal's web site is located at http://www.elsevier.com/locate/scitotenv
 
dc.publisher.placeNetherlands
 
dc.relation.ispartofScience of the Total Environment
 
dc.relation.referencesReferences in Scopus
 
dc.subject.meshAir - standards
 
dc.subject.meshArchitecture as Topic
 
dc.subject.meshCities
 
dc.subject.meshEnvironment
 
dc.subject.meshModels, Theoretical
 
dc.titleOn the contribution of mean flow and turbulence to city breathability: the case of long streets with tall buildings
 
dc.typeArticle
 
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<contributor.author>Di Sabatino, S</contributor.author>
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Author Affiliations
  1. The University of Hong Kong
  2. Hogskolan i Gavle
  3. null
  4. Guangzhou University