Three-Dimensional Mapping of Air Flow at an Urban Canyon Intersection

Abstract

In this experimental work both qualitative (flow visualisation) and quantitative (laser Doppler anemometry) methods were applied in a wind tunnel in order to describe the complex 3-dimensional flow field in a real environment (a street canyon intersection). The main aim was an examination of the mean flow, turbulence and flow pathlines characterising a complex 3-dimensional urban location. The experiments highlighted the complexity of the observed flows, particularly in the upwind region of the intersection. In this complex and realistic situation some details of the upwind flow, such as the presence of two tall towers, play an important role in defining the flow field within the intersection, particularly at roof level. This effect is likely to have a strong influence on the mass exchange mechanism between the canopy flow and the air aloft, and therefore the distribution of pollutants. This strong interaction between the flows inside and outside the urban canopy is currently neglected in most state-of-the-art local scale dispersion models.

Influence of urban morphology on air flow over building arrays

“…The results have been extremely useful in identifying shortcomings of current modelling approaches (Carpentieri et al, 2012) and important phenomena likely to have a major impact on flow and dispersion (Carpentieri et al, 2009;Carpentieri and Robins, 2010). However, more systematic approaches are needed to make possible the quantification and identification of the relative importance of the various parameters involved.…”

“…The latter aspect (i.e. the effect of tall buildings) has been sporadically studied in the past, and previous experiments have already highlighted its importance (Carpentieri et al, 2009;Carpentieri and Robins, 2010;Heist et al, 2009;Brixey et al, 2009). However, no modelling approaches have been proposed to take account of associated flow and dispersion phenomena.…”

“…The starting point for the design of the models was the 1:200 scale model of the DAPPLE field site in central London (Arnold et al 2004, Carpentieri et al 2009. A substantial amount of data has been gathered in wind tunnel experiments, field tests and numerical simulations for the DAPPLE site, and these data can be used in future as comparison for the simpler models.…”

“…These properties depend strongly on the local geometry and existing models generally relate them to the mean building height (H b ) and the lambda parameters (λ p , and λ f , see above). Recent studies (Carpentieri et al 2009(Carpentieri et al , 2012aCarpentieri and Robins, 2010;Harms et al, 2011;Klein et al, 2011), however, have highlighted the complexity of the flow and dispersion fields in actual urban geometries (as opposed to idealised building arrangements). It is clear from such studies that more parameters (such as building height variability and building aspect ratio) should be taken into account for a more accurate prediction of flow and dispersion in actual urban canopies.…”

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

“…Minor departures from symmetry were found to result in large differences in the exchanges. Carpentieri et al [27], making wind-tunnel measurements at an asymmetric intersection, observed complex 3D effects that enhanced the interaction of the canopy flow with the overlying flow.…”