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Article: Large-Eddy Simulation of Flow and Pollutant Transports in and Above Two-Dimensional Idealized Street Canyons

TitleLarge-Eddy Simulation of Flow and Pollutant Transports in and Above Two-Dimensional Idealized Street Canyons
Authors
KeywordsLarge-eddy simulation
Pollutant removal
Quadrant analysis
Turbulence
Urban street canyons
Issue Date2011
PublisherSpringer Verlag Dordrecht. The Journal's web site is located at http://springerlink.metapress.com/openurl.asp?genre=journal&issn=0006-8314
Citation
Boundary-Layer Meteorology, 2011, v. 139 n. 3, p. 411-437 How to Cite?
AbstractA large-eddy simulation (LES) model, using the one-equation subgrid-scale (SGS) parametrization, was developed to study the flow and pollutant transport in and above urban street canyons. Three identical two-dimensional (2D) street canyons of unity aspect ratio, each consisting of a ground-level area source of constant pollutant concentration, are evenly aligned in a cross-flow in the streamwise direction x. The flow falls into the skimming flow regime. A larger computational domain is adopted to accurately resolve the turbulence above roof level and its influence on the flow characteristics in the street canyons. The LES calculated statistics of wind and pollutant transports agree well with other field, laboratory and modelling results available in the literature. The maximum wind velocity standard deviations σi in the streamwise (σu), spanwise (σv) and vertical (σw) directions are located near the roof-level windward corners. Moreover, a second σw peak is found at z ≈ 1.5h (h is the building height) over the street canyons. Normalizing σi by the local friction velocity u*, it is found that σu/u* ≈ 1.8, σv/u* ≈ 1.3 and σw/u* ≈ 1.25 exhibiting rather uniform values in the urban roughness sublayer. Quadrant analysis of the vertical momentum flux u′′w′′ shows that, while the inward and outward interactions are small, the sweeps and ejections dominate the momentum transport over the street canyons. In the x direction, the two-point correlations of velocity Rv,x and Rw,x drop to zero at a separation larger than h but Ru,x (= 0.2) persists even at a separation of half the domain size. Partitioning the convective transfer coefficient ΩT of pollutant into its removal and re-entry components, an increasing pollutant re-entrainment from 26.3 to 43.3% in the x direction is revealed, suggesting the impact of background pollutant on the air quality in street canyons. © 2011 The Author(s).
Persistent Identifierhttp://hdl.handle.net/10722/145064
ISSN
2015 Impact Factor: 2.455
2015 SCImago Journal Rankings: 1.726
ISI Accession Number ID
Funding AgencyGrant Number
University Research Committee, University of Hong Kong200811159170
Funding Information:

This project is partly supported by the University Research Committee Seed Funding Programme of Basic Research of the University of Hong Kong 200811159170. The authors are also grateful to the technical support from Mr. W. K. Kwan, Mr. Frankie T. F. Cheung and Ms. Lilian Y. L. Chan with the Computer Centre, The University of Hong Kong.

References

 

DC FieldValueLanguage
dc.contributor.authorCheng, WCen_HK
dc.contributor.authorLiu, CHen_HK
dc.date.accessioned2012-02-21T05:44:12Z-
dc.date.available2012-02-21T05:44:12Z-
dc.date.issued2011en_HK
dc.identifier.citationBoundary-Layer Meteorology, 2011, v. 139 n. 3, p. 411-437en_HK
dc.identifier.issn0006-8314en_HK
dc.identifier.urihttp://hdl.handle.net/10722/145064-
dc.description.abstractA large-eddy simulation (LES) model, using the one-equation subgrid-scale (SGS) parametrization, was developed to study the flow and pollutant transport in and above urban street canyons. Three identical two-dimensional (2D) street canyons of unity aspect ratio, each consisting of a ground-level area source of constant pollutant concentration, are evenly aligned in a cross-flow in the streamwise direction x. The flow falls into the skimming flow regime. A larger computational domain is adopted to accurately resolve the turbulence above roof level and its influence on the flow characteristics in the street canyons. The LES calculated statistics of wind and pollutant transports agree well with other field, laboratory and modelling results available in the literature. The maximum wind velocity standard deviations σi in the streamwise (σu), spanwise (σv) and vertical (σw) directions are located near the roof-level windward corners. Moreover, a second σw peak is found at z ≈ 1.5h (h is the building height) over the street canyons. Normalizing σi by the local friction velocity u*, it is found that σu/u* ≈ 1.8, σv/u* ≈ 1.3 and σw/u* ≈ 1.25 exhibiting rather uniform values in the urban roughness sublayer. Quadrant analysis of the vertical momentum flux u′′w′′ shows that, while the inward and outward interactions are small, the sweeps and ejections dominate the momentum transport over the street canyons. In the x direction, the two-point correlations of velocity Rv,x and Rw,x drop to zero at a separation larger than h but Ru,x (= 0.2) persists even at a separation of half the domain size. Partitioning the convective transfer coefficient ΩT of pollutant into its removal and re-entry components, an increasing pollutant re-entrainment from 26.3 to 43.3% in the x direction is revealed, suggesting the impact of background pollutant on the air quality in street canyons. © 2011 The Author(s).en_HK
dc.languageengen_US
dc.publisherSpringer Verlag Dordrecht. The Journal's web site is located at http://springerlink.metapress.com/openurl.asp?genre=journal&issn=0006-8314en_HK
dc.relation.ispartofBoundary-Layer Meteorologyen_HK
dc.rightsThe Author(s)en_US
dc.rightsCreative Commons: Attribution 3.0 Hong Kong Licenseen_US
dc.subjectLarge-eddy simulationen_HK
dc.subjectPollutant removalen_HK
dc.subjectQuadrant analysisen_HK
dc.subjectTurbulenceen_HK
dc.subjectUrban street canyonsen_HK
dc.titleLarge-Eddy Simulation of Flow and Pollutant Transports in and Above Two-Dimensional Idealized Street Canyonsen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4551/resserv?sid=springerlink&genre=article&atitle=Large-Eddy Simulation of Flow and Pollutant Transports in and Above Two-Dimensional Idealized Street Canyons&title=Boundary-Layer Meteorology&issn=00068314&date=2011-06-01&volume=139&issue=3& spage=411&authors=W. C. Cheng, Chun-Ho Liuen_US
dc.identifier.emailLiu, CH:chliu@hkucc.hku.hken_HK
dc.identifier.authorityLiu, CH=rp00152en_HK
dc.description.naturepublished_or_final_versionen_US
dc.identifier.doi10.1007/s10546-010-9584-yen_HK
dc.identifier.scopuseid_2-s2.0-79955523123en_HK
dc.identifier.hkuros195785-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-79955523123&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume139en_HK
dc.identifier.issue3en_HK
dc.identifier.spage411en_HK
dc.identifier.epage437en_HK
dc.identifier.eissn1573-1472en_US
dc.identifier.isiWOS:000290034400003-
dc.publisher.placeNetherlandsen_HK
dc.description.otherSpringer Open Choice, 21 Feb 2012en_US
dc.identifier.scopusauthoridCheng, WC=24283028300en_HK
dc.identifier.scopusauthoridLiu, CH=36065161300en_HK
dc.identifier.citeulike8644811-

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