Article: Passive urban ventilation by combined buoyancy-driven slope flow and wall flow: parametric CFD studies on idealized city models
| Title | Passive urban ventilation by combined buoyancy-driven slope flow and wall flow: parametric CFD studies on idealized city models |
|---|---|
| Authors | Luo, Z1 Li, Y1 |
| Keywords | Age of air Air change rates Background winds Building height Buoyancy driven flows |
| Issue Date | 2011 |
| Publisher | Pergamon. The Journal's web site is located at http://www.elsevier.com/locate/atmosenv |
| Citation | Atmospheric Environment, 2011, v. 45 n. 32, p. 5946-5956 [How to Cite?] DOI: http://dx.doi.org/10.1016/j.atmosenv.2011.04.010 |
| 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° 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. |
| ISSN | 1352-2310 2011 Impact Factor: 3.465 2011 SCImago Journal Rankings: 0.167 |
| DOI | http://dx.doi.org/10.1016/j.atmosenv.2011.04.010 |
| References | References in Scopus |
| dc.contributor.author | Luo, Z | ||||
|---|---|---|---|---|---|
| dc.contributor.author | Li, Y | ||||
| dc.date.accessioned | 2012-08-08T08:45:34Z | ||||
| dc.date.available | 2012-08-08T08:45:34Z | ||||
| dc.date.issued | 2011 | ||||
| dc.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° 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.nature | Link_to_subscribed_fulltext | ||||
| dc.identifier.citation | Atmospheric 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.doi | http://dx.doi.org/10.1016/j.atmosenv.2011.04.010 | ||||
| dc.identifier.epage | 5956 | ||||
| dc.identifier.hkuros | 209897 | ||||
| dc.identifier.isi | WOS:000295607300032
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.issn | 1352-2310 2011 Impact Factor: 3.465 2011 SCImago Journal Rankings: 0.167 | ||||
| dc.identifier.issue | 32 | ||||
| dc.identifier.scopus | eid_2-s2.0-81155162506 | ||||
| dc.identifier.spage | 5946 | ||||
| dc.identifier.uri | http://hdl.handle.net/10722/157155 | ||||
| dc.identifier.volume | 45 | ||||
| dc.language | eng | ||||
| dc.publisher | Pergamon. The Journal's web site is located at http://www.elsevier.com/locate/atmosenv | ||||
| dc.publisher.place | United Kingdom | ||||
| dc.relation.ispartof | Atmospheric Environment | ||||
| dc.relation.references | References in Scopus | ||||
| dc.subject | Age of air | ||||
| dc.subject | Air change rates | ||||
| dc.subject | Background winds | ||||
| dc.subject | Building height | ||||
| dc.subject | Buoyancy driven flows | ||||
| dc.title | Passive urban ventilation by combined buoyancy-driven slope flow and wall flow: parametric CFD studies on idealized city models | ||||
| dc.type | Article |
Author Affiliations
- The University of Hong Kong