Large-Eddy Simulation of Pollutant Removal from a Three-Dimensional Street Canyon

Michioka, Takenobu; Takimoto, Hiroshi; Sato, Ayumu

doi:10.1007/s10546-013-9870-6

Cited by 56 publications

(38 citation statements)

References 39 publications

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“…14, which suggests the dominating mechanism responsible for pollutant removal has developed after three streets. Accordingly, in (periodic) simulations of fully-developed flow over street canyons qualitatively similar joint p.d.f.s are found (Michioka et al 2014). From the results presented here it can be concluded that ventilation of street canyons is associated with low momentum regions passing the street canyons.…”

Section: Pollutant Dispersion Mechanismssupporting

confidence: 81%

“…However, the local values of w are relatively small and the agreement with the experiment is satisfactory. It is found that, similar to Michioka et al (2014), w c is always positive at the top of the canopy, i.e. turbulence always acts to remove pollutants from the street canyons.…”

Section: Pollutant Dispersion Mechanismsmentioning

confidence: 62%

“…Tomas et al (2016) show that up to 14h downstream of a rural-to-urban roughness transition the advective pollutant flux remains significant. Furthermore, Michioka et al (2011Michioka et al ( , 2014 conclude that street-canyon ventilation mostly takes place when low momentum regions pass over the canyon, and they suggest that these regions are of small scale compared to the coherent structures in the outer region and are generated close to the top of the canopy.…”

Section: Introductionmentioning

confidence: 99%

“…For example, Cheng and Castro (2002b) carried out experiments on turbulent boundary layers where the complete bottom wall of the wind tunnel was covered with cubical roughness elements, thereby representing the flow over an urban area. In multiple simulation studies the fully-developed character of the flow is implicitly assumed by employing periodic boundary conditions in the horizontal directions (e.g., Coceal et al 2006;Michioka et al 2014;Boppana et al 2014). However, in reality the surface roughness changes, e.g.…”

Section: Introductionmentioning

confidence: 99%

“…In order to obtain insight in pollutant dispersion mechanisms, Michioka et al (2014) performed large-eddy simulations (LES) on fully-developed flow over an array of obstacles with various aspect ratios l/ h, where l is the spanwise obstacle length and h is the obstacle height. They conclude that for fully-developed conditions the turbulent pollutant flux is the main contributor to street-canyon ventilation, although the ratio of the turbulent to the advective pollutant flux does change slightly for different aspect ratios.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Pollutant Dispersion in Boundary Layers Exposed to Rural-to-Urban Transitions: Varying the Spanwise Length Scale of the Roughness

Tomas

Eisma

Pourquié

et al. 2017

Boundary-Layer Meteorol

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Both large-eddy simulations (LES) and water-tunnel experiments, using simultaneous stereoscopic particle image velocimetry and laser-induced fluorescence, have been used to investigate pollutant dispersion mechanisms in regions where the surface changes from rural to urban roughness. The urban roughness was characterized by an array of rectangular obstacles in an in-line arrangement. The streamwise length scale of the roughness was kept constant, while the spanwise length scale was varied by varying the obstacle aspect ratio l/ h between 1 and 8, where l is the spanwise dimension of the obstacles and h is the height of the obstacles. Additionally, the case of two-dimensional roughness (riblets) was considered in LES. A smooth-wall turbulent boundary layer of depth 10h was used as the approaching flow, and a line source of passive tracer was placed 2h upstream of the urban canopy. The experimental and numerical results show good agreement, while minor discrepancies are readily explained. It is found that for l/ h = 2 the drag induced by the urban canopy is largest of all considered cases, and is caused by a large-scale secondary flow. In addition, due to the roughness transition the vertical advective pollutant flux is the main ventilation mechanism in the first three streets. Furthermore, by means of linear stochastic estimation the mean flow structure is identified that is responsible for street-canyon ventilation for the sixth street and onwards. Moreover, it is shown that the vertical length scale of this structure increases with increasing aspect ratio of the obstacles in the canopy, while the streamwise length scale does not show a similar trend.

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Section: Pollutant Dispersion Mechanismssupporting

confidence: 81%

Section: Pollutant Dispersion Mechanismsmentioning

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Pollutant Dispersion in Boundary Layers Exposed to Rural-to-Urban Transitions: Varying the Spanwise Length Scale of the Roughness

Tomas

Eisma

Pourquié

et al. 2017

Boundary-Layer Meteorol

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Effects of air-side freestream turbulence on the development of air–liquid surface waves

et al. 2020

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Stable Stratification Effects on Flow and Pollutant Dispersion in Boundary Layers Entering a Generic Urban Environment

Tomas¹,

Pourquié²,

Jonker

2016

Boundary-Layer Meteorol

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Large-eddy simulations (LES) are used to investigate the effect of stable stratification on rural-to-urban roughness transitions. Smooth-wall turbulent boundary layers are subjected to a generic urban roughness consisting of cubes in an in-line arrangement. Two line sources of pollutant are added to investigate the effect on pollutant dispersion. Firstly, the LES method is validated with data from wind-tunnel experiments on fully-developed flow over cubical roughness. Good agreement is found for the vertical profiles of the mean streamwise velocity component and mean Reynolds stress. Subsequently, roughness transition simulations are done for both neutral and stable conditions. Results are compared with fully-developed simulations with conventional double-periodic boundary conditions. In stable conditions, at the end of the domain the streamwise velocity component has not yet reached the fully-developed state even though the surface forces are nearly constant. Moreover, the internal boundary layer is shallower than in the neutral case. Furthermore, an investigation of the turbulence kinetic energy budget shows that the buoyancy destruction term is reduced in the internal boundary layer, above which it is equal to the undisturbed (smooth wall) value. In addition, in stable conditions pollutants emitted above the urban canopy enter the canopy farther downstream due to decreased vertical mixing. Pollutants emitted below the top of the urban canopy are 85 % higher in concentration in stable conditions mostly due to decreased advection. If this is taken into account concentrations remain 17 % greater in stable conditions due to less rapid internal boundary-layer growth. Finally, it

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Large-Eddy Simulation of Pollutant Removal from a Three-Dimensional Street Canyon

Cited by 56 publications

References 39 publications

Pollutant Dispersion in Boundary Layers Exposed to Rural-to-Urban Transitions: Varying the Spanwise Length Scale of the Roughness

Pollutant Dispersion in Boundary Layers Exposed to Rural-to-Urban Transitions: Varying the Spanwise Length Scale of the Roughness

Effects of air-side freestream turbulence on the development of air–liquid surface waves

Stable Stratification Effects on Flow and Pollutant Dispersion in Boundary Layers Entering a Generic Urban Environment

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