Parameters characterising dispersion in the near wake of buildings

Fackrell, J.E.

doi:10.1016/0167-6105(84)90051-5

Cited by 69 publications

(46 citation statements)

References 11 publications

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“…Vertical profiles of standard deviation of horizontal and vertical velocities are maintained constant with a slight peak at 2.5 cm from the ground. The reference Reynolds number, based on the free stream velocity (v 1 ) and characteristics length scale, H Ã b (length scale based on the obstacle frontal area; H Ã b ¼ ðWHÞ 1=2 ) was Re = 12,600, which is sufficient to satisfy Reynolds number independency criteria of Re % 4000 (Halitsky, 1968;Fackrell and Pearce, 1981;Snyder, 1981;Yee et al, 2006). Although, such high Reynolds number satisfies the conditions to simulate real world atmospheric dispersion in the water channels, it needs to be noted that due to the nature of laboratory flow simulation systems, flows in water channels are more coherent than real atmosphere.…”

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confidence: 99%

Sound wall barriers: Near roadway dispersion under neutrally stratified boundary layer

Pournazeri

Princevac

2015

Transportation Research Part D: Transport and Environment

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a b s t r a c tWith the passage of California Senate Bill 375, which motivates infill development near transit hubs, there is the potential to increase vehicle congestion in residential communities and increase in human exposure to toxic mobile source pollutants. Among all the mitigation strategies that protect near roadway residents from health-affecting vehicular emissions (e.g. separating sensitive receptors from high traffic roadways), this paper discusses the impact of sound wall barriers (SBs) in reducing the air pollution exposure of nearby residents. To date, there have been some studies done to understand the impact of these structures on dispersion of vehicular emissions; however, no definitive conclusion has been drawn yet. The main objective of this paper is to provide more information and details on flow and dispersion affected by barriers through a systematic laboratory simulation of plume dispersion using a water channel. Three sets of experiments were conducted: (1) plume visualizations, (2) plume concentration measurements, and (3) flow velocity measurements. Results from this study shows that the deployment of sound barriers induces a recirculating flow over the roadway which transports the surface released emissions to the upwind side of the roadway, and then shifts the plume upward through an induced updraft motion. Plume visualizations clearly demonstrate that the presence of SBs induce significant vertical mixing and updraft motion on the roadway which increases the initial plume dilution and plume height and consequently results in reduced downwind ground level concentrations. Although different SB configurations result in different localized flow patterns, the dispersion pattern does not change significantly after several SB heights downwind of the roadway.Ó 2015 Elsevier Ltd. All rights reserved. IntroductionNumerous epidemiological studies have shown that long-term exposure to outdoor air pollution increases the risk of respiratory diseases, birth defects, premature mortality, cardiovascular disease, and cancer (Dockery and Pope, 1994;Harrison et al., 1999;Wilhelm and Ritz, 2003;Peters et al., 2004;Jerrett et al., 2005;McConnell et al., 2006). Houston et al. (2006) showed that more than 24,000 childcare centers in California are within 200 m of highly trafficked roadways with more than 50,000 vehicles per day. A statistical analysis has shown that children diagnosed with asthma are more likely to live within 500 m of major roadways (Edwards et al., 1994).

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confidence: 99%

Sound wall barriers: Near roadway dispersion under neutrally stratified boundary layer

Pournazeri

Princevac

2015

Transportation Research Part D: Transport and Environment

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“…Clearly, the most important of these parameters is L R and, fortunately, established relations exist to describe this length in terms of the building height, width, and depth (h, b and l, respectively). Fackrell (1984) proposed the following empirical expression for L R , after measuring the parameter for a large variety of different building shapes with b/ h ranging from 0.5 to 5 and l/ h ranging from 0.3 to 3:…”

Section: Idealized Descriptions Of Individual Building Wakesmentioning

confidence: 99%

Estimating Aerodynamic Parameters of Urban-Like Surfaces with Heterogeneous Building Heights

Millward-Hopkins

Tomlin

et al. 2011

Boundary-Layer Meteorol

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There are many geometrical factors than can influence the aerodynamic parameters of urban surfaces and hence the vertical wind profiles found above. The knowledge of these parameters has applications in numerous fields, such as dispersion modelling, wind loading calculations, and estimating the wind energy resource at urban locations. Using quasiempirical modelling, we estimate the dependence of the aerodynamic roughness length and zero-plane displacement for idealized urban surfaces, on the two most significant geometrical characteristics; surface area density and building height variability. A validation of the spatially-averaged, logarithmic wind profiles predicted by the model is carried out, via comparisons with available wind-tunnel and numerical data for arrays of square based blocks of uniform and heterogeneous heights. The model predicts two important properties of the aerodynamic parameters of surfaces of heterogeneous heights that have been suggested by experiments. Firstly, the zero-plane displacement of a heterogeneous array can exceed the surface mean building height significantly. Secondly, the characteristic peak in roughness length with respect to surface area density becomes much softer for heterogeneous arrays compared to uniform arrays, since a variation in building height can prevent a skimming flow regime from occurring. Overall the simple model performs well against available experimental data and may offer more accurate estimates of surface aerodynamic parameters for complex urban surfaces compared to models that do not include height variability.

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“…where γV = γ'v'(being γ another constant), and T w is the time scale of pollutant decay, defined as T w = β h / V; the empirical constant β can be taken as ≈ 5 (Fackrell, 1984). Equation (2) can be integrated as:…”

Section: Approaches Derived From Building Wakesmentioning

confidence: 99%

An overview of experimental results and dispersion modelling of nanoparticles in the wake of moving vehicles

Carpentieri

Kumar

Robins

2011

Environmental Pollution

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Parameters characterising dispersion in the near wake of buildings

Cited by 69 publications

References 11 publications

Sound wall barriers: Near roadway dispersion under neutrally stratified boundary layer

Sound wall barriers: Near roadway dispersion under neutrally stratified boundary layer

Estimating Aerodynamic Parameters of Urban-Like Surfaces with Heterogeneous Building Heights

An overview of experimental results and dispersion modelling of nanoparticles in the wake of moving vehicles

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