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Article: On the contribution of mean flow and turbulence to city breathability: the case of long streets with tall buildings

TitleOn the contribution of mean flow and turbulence to city breathability: the case of long streets with tall buildings
Authors
Issue Date2012
PublisherElsevier BV. The Journal's web site is located at http://www.elsevier.com/locate/scitotenv
Citation
Science of the Total Environment, 2012, v. 416, p. 362-373 How to Cite?
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.
Persistent Identifierhttp://hdl.handle.net/10722/157171
ISSN
2014 Impact Factor: 4.099
2013 SCImago Journal Rankings: 1.530
ISI Accession Number ID
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.

References

 

DC FieldValueLanguage
dc.contributor.authorHang, Jen_US
dc.contributor.authorLi, Yen_US
dc.contributor.authorBuccolieri, Ren_US
dc.contributor.authorSandberg, Men_US
dc.contributor.authorDi Sabatino, Sen_US
dc.date.accessioned2012-08-08T08:45:38Z-
dc.date.available2012-08-08T08:45:38Z-
dc.date.issued2012en_US
dc.identifier.citationScience of the Total Environment, 2012, v. 416, p. 362-373en_US
dc.identifier.issn0048-9697en_US
dc.identifier.urihttp://hdl.handle.net/10722/157171-
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.en_US
dc.languageengen_US
dc.publisherElsevier BV. The Journal's web site is located at http://www.elsevier.com/locate/scitotenven_US
dc.relation.ispartofScience of the Total Environmenten_US
dc.subject.meshAir - standardsen_US
dc.subject.meshArchitecture as Topicen_US
dc.subject.meshCitiesen_US
dc.subject.meshEnvironmenten_US
dc.subject.meshModels, Theoreticalen_US
dc.titleOn the contribution of mean flow and turbulence to city breathability: the case of long streets with tall buildingsen_US
dc.typeArticleen_US
dc.identifier.emailHang, J: hangjian@hku.hken_US
dc.identifier.emailLi, Y: liyg@hkucc.hku.hk-
dc.identifier.emailBuccolieri, R: riccardo.buccolieri@unisalento.it-
dc.identifier.authorityLi, Y=rp00151en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.doi10.1016/j.scitotenv.2011.12.016en_US
dc.identifier.pmid22226399en_US
dc.identifier.scopuseid_2-s2.0-84856226321en_US
dc.identifier.hkuros205319-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-84856226321&selection=ref&src=s&origin=recordpageen_US
dc.identifier.volume416en_US
dc.identifier.spage362en_US
dc.identifier.epage373en_US
dc.identifier.isiWOS:000301155200041-
dc.publisher.placeNetherlandsen_US
dc.identifier.scopusauthoridDi Sabatino, S=22979043500en_US
dc.identifier.scopusauthoridSandberg, M=35585315900en_US
dc.identifier.scopusauthoridBuccolieri, R=22978582300en_US
dc.identifier.scopusauthoridLi, Y=7502094052en_US
dc.identifier.scopusauthoridHang, J=35240092500en_US
dc.identifier.citeulike10233888-

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