Street canyon ventilation and atmospheric turbulence

Salizzoni, Pietro; Soulhac, Lionel; Méjean, P.

doi:10.1016/j.atmosenv.2009.06.045

Cited by 120 publications

(73 citation statements)

References 20 publications

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“…Quadrant analysis of turbulent pollutant fluxes have shown that the ejections and sweeps dominate while sweeps contribute slightly more than ejections near the roof level [38], while Michioka et al [39] indicated that a large amount of pollutant is removed from the canyon by ejection due to the large-scale coherent structures. The turbulent intensity of the approaching flow could also directly influence pollutant removal from street canyons, as demonstrated in wind-tunnel experiments [34] and numerically [40]. The average pollutant concentration within the street canyon decreases as the friction velocity, u * , of the approaching turbulent flow increases [34,41].…”

Section: Flow and Dispersion Under Neutral Stratification Conditionsmentioning

confidence: 95%

“…The turbulent intensity of the approaching flow could also directly influence pollutant removal from street canyons, as demonstrated in wind-tunnel experiments [34] and numerically [40]. The average pollutant concentration within the street canyon decreases as the friction velocity, u * , of the approaching turbulent flow increases [34,41]. This is a direct result of the friction velocity being a measure of the mixing processes and of the bulk exchange of fluid near the top of the street canyon that will reduce the concentrations within the street canyon.…”

Section: Flow and Dispersion Under Neutral Stratification Conditionsmentioning

confidence: 99%

“…The unsteady condition of the flow results in a flapping motion of the shear layer and a subsequent intermittent inflow of turbulent structures into the canyon that induces the bulk transfer between the canyon and the external flow [34].…”

Section: Flow and Dispersion Under Neutral Stratification Conditionsmentioning

confidence: 99%

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Transport processes in and above two-dimensional urban street canyons under different stratification conditions: results from numerical simulation

Britter

Norford

2014

Environ Fluid Mech

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Thermal stratification (neutral, unstable and stable) plays an important role in determining the transport processes in and above urban street canyons. This paper summarizes the recent findings of the effect of thermal stratification on the transport of momentum, heat, and pollutants in the two-dimensional (2D) urban street canyons in the skimming flow regime. Special attention is paid to the results from large-eddy simulations (LESs), while other experimental and numerical results are referred to when necessary. With increasing Richardson number, Ri, the drag coefficient of the 2D street canyon as felt by the overlying atmosphere decreases in a linear manner. Under neutral and stable stratification, a nearly constant drag coefficient of 0.02 is predicted by the LESs. Under unstable stratification, the turbulent pollutant transport is dominated by organized turbulent motions (ejections and sweeps), while under stable stratification, the unorganized turbulent motion (inward interactions) plays a more important role and the sweeps are inhibited. The unstable stratification condition also enhances the ejections of turbulent pollutant flux, especially at the leeward roof-level corner, where the ejections dominate the turbulent pollutant flux, outweighing the sweeps. With increasing Ri, both the heat (area active scalar source) and pollutant (line passive scalar source) transfer coefficients decrease towards a state where the transfer coefficients become zero at Ri ≈ 0.5. It should be noted that, due to the limit of the 2D street canyon configuration discussed in this paper, great caution should be taken when generalising the conclusions drawn here.

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Section: Flow and Dispersion Under Neutral Stratification Conditionsmentioning

confidence: 95%

Section: Flow and Dispersion Under Neutral Stratification Conditionsmentioning

confidence: 99%

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Transport processes in and above two-dimensional urban street canyons under different stratification conditions: results from numerical simulation

Britter

Norford

2014

Environ Fluid Mech

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“…The problem of the pollution transport within the built-up areas were summarised in several recent works [3][4][5]. A mass exchange between street canyon and external atmospheric flow and the influence of the external turbulence intensity on the scalar transfer from the canyon was investigated in [6]. A pollution transfer within a model of a real street intersection in Central London (DAPPLE series of projects) was balanced in [7].…”

Section: Introductionmentioning

confidence: 99%

Ventilation of idealised urban area, LES and wind tunnel experiment

Kukačka

Fuka

Nosek

et al. 2014

EPJ Web of Conferences

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Abstract. In order to estimate the ventilation of vehicle pollution within street canyons, a wind tunnel experiment and a large eddy simulation (LES) was performed. A model of an idealised urban area with apartment houses arranged to courtyards was designed according to common Central European cities. In the wind tunnel, we assembled a set-up for simultaneous measurement of vertical velocity and tracer gas concentration. Due to the vehicle traffic emissions modelling, a new line source of tracer gas was designed and built into the model. As a computational model, the LES model solving the incompressible Navier-Stokes equations was used. In this paper, we focused on the street canyon with the line source situated perpendicular to an approach flow. Vertical and longitudinal velocity components of the flow with the pollutant concentration were obtained from two horizontal grids placed in different heights above the street canyon. Vertical advective and turbulent pollution fluxes were computed from the measured data as ventilation characteristics. Wind tunnel and LES data were qualitatively compared. A domination of advective pollution transport within the street canyon was determined. However, the turbulent transport with an opposite direction to the advective played a significant role within and above the street canyon.

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“…Most of the systematic studies on building arrays involve the use of cuboidal obstacles (Cheng and Castro, 2002;Cheng et al, 2007) or relatively deep and long street canyons (Kastner- Klein and Plate, 1999;Salizzoni et al, 2009). The few papers that consider a more realistic urban form usually tend to focus on diagonally symmetric buildings (width = length), so that fewer wind directions are needed to completely characterise flow and dispersion (Garbero et al, 2010).…”

Section: Introductionmentioning

confidence: 99%