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Article: Turbulent transport mechanism in the roughness sublayers over idealized urban areas and its implication to street-level ventilation

TitleTurbulent transport mechanism in the roughness sublayers over idealized urban areas and its implication to street-level ventilation
Authors
KeywordsAerodynamic resistance
Drag coefficient Cd
Inertial sublayer (ISL)
Roughness sublayer (RSL)
Turbulent transport
Wind tunnel experiment
Issue Date29-Oct-2023
PublisherElsevier
Citation
Sustainable Cities and Society, 2024, v. 100 How to Cite?
Abstract

Turbulence in the roughness sublayer (RSL) is inhomogeneous compared with that in the inertial sublayer (ISL) of the atmospheric surface layer (ASL) over urban areas. Drag coefficient Cd, which measures aerodynamic roughness, is employed in this paper to examine how (idealized) urban morphology influences ASL dynamics and transport. Wind tunnel experiments are conducted to study the flows and turbulence in response to different configurations of (identical) roughness elements. Statistics, quadrant analysis, and tilt angle evidence the more efficient RSL transport over rougher surfaces even the winds are slower. Although the power spectra of streamwise u’’ and vertical w’’ fluctuating velocities are rather insensitive to Cd, their cospectrum shows a secondary peak at small motion scales λx (≤ 0.1δ where δ is the thickness of turbulent boundary layer) along with the primary peak at integral length scale Λx (≈ δ). It is thus suggested that, regardless of the turbulence intensity, RSL streamwise and vertical winds are more correlated, enhancing the transport. Amplitude (AM) and frequency (FM) modulations signify the positive correlation between RSL large and small motion scales which is amplified over rougher surfaces. Furthermore, RSL turbulence kinetic energy (TKE) production (entrainment) increases with decreasing (increasing) Cd, fostering the basic mechanism of street-level ventilation.


Persistent Identifierhttp://hdl.handle.net/10722/339913
ISSN
2023 Impact Factor: 10.5
2023 SCImago Journal Rankings: 2.545
ISI Accession Number ID

 

DC FieldValueLanguage
dc.contributor.authorWang, Ruiqi-
dc.contributor.authorLiu, Chun-Ho-
dc.contributor.authorLi, Fei-
dc.contributor.authorMo, Ziwei-
dc.date.accessioned2024-03-11T10:40:16Z-
dc.date.available2024-03-11T10:40:16Z-
dc.date.issued2023-10-29-
dc.identifier.citationSustainable Cities and Society, 2024, v. 100-
dc.identifier.issn2210-6707-
dc.identifier.urihttp://hdl.handle.net/10722/339913-
dc.description.abstract<p>Turbulence in the roughness sublayer (RSL) is inhomogeneous compared with that in the inertial sublayer (ISL) of the atmospheric surface layer (ASL) over urban areas. Drag coefficient <em>C<sub>d</sub></em>, which measures aerodynamic roughness, is employed in this paper to examine how (idealized) urban morphology influences ASL dynamics and transport. Wind tunnel experiments are conducted to study the flows and turbulence in response to different configurations of (identical) roughness elements. Statistics, quadrant analysis, and tilt angle evidence the more efficient RSL transport over rougher surfaces even the winds are slower. Although the power spectra of streamwise <em>u’’</em> and vertical <em>w’’</em> fluctuating velocities are rather insensitive to <em>C<sub>d</sub></em>, their cospectrum shows a secondary peak at small motion scales <em>λ<sub>x</sub></em> (≤ 0.1<em>δ</em> where <em>δ</em> is the thickness of turbulent boundary layer) along with the primary peak at integral length scale Λ<em><sub>x</sub></em> (≈ <em>δ</em>). It is thus suggested that, regardless of the turbulence intensity, RSL streamwise and vertical winds are more correlated, enhancing the transport. Amplitude (AM) and frequency (FM) modulations signify the positive correlation between RSL large and small motion scales which is amplified over rougher surfaces. Furthermore, RSL turbulence kinetic energy (TKE) production (entrainment) increases with decreasing (increasing) Cd, fostering the basic mechanism of street-level ventilation.<br></p>-
dc.languageeng-
dc.publisherElsevier-
dc.relation.ispartofSustainable Cities and Society-
dc.rightsThis work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.-
dc.subjectAerodynamic resistance-
dc.subjectDrag coefficient Cd-
dc.subjectInertial sublayer (ISL)-
dc.subjectRoughness sublayer (RSL)-
dc.subjectTurbulent transport-
dc.subjectWind tunnel experiment-
dc.titleTurbulent transport mechanism in the roughness sublayers over idealized urban areas and its implication to street-level ventilation-
dc.typeArticle-
dc.identifier.doi10.1016/j.scs.2023.105030-
dc.identifier.scopuseid_2-s2.0-85175706444-
dc.identifier.volume100-
dc.identifier.eissn2210-6715-
dc.identifier.isiWOS:001111689500001-
dc.identifier.issnl2210-6707-

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