EXP 1-2 Description: Difference between revisions
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All major flow (mean velocity and turbulence statistics, including momentum fluxes) and pollutant (mean and standard deviation of concentration) concentration qunatities, as well as turbulent and mean (advective) pollutant fluxes, were measured at the top ( labelled T, Fig. 2c) and lateral (Fig. 2d) openings of the studied street canyon. Due to the uneven roof height, all quantities were measured at two heights in the case of the top openings. The first height was chosen at z/H = 0.6, which corresponds to the lowest street canyon wall (without taking roof pitches into account, see Fig. 2d). This height thus enclosed each street canyon of the non-uniform urban model from top. The second at z/H = 1 was chosen as the reference height for both urban models. In the case of the lateral openings, all quantitates were measured at the right (labelled R when viewed from downstream ) and left (labelled L) openings of each street canyon studied up to the height z/H = 0.6. At the top openings, the longitudinal (u) and vertical (w) velocity components were measured simultaneously, while at the lateral openings, the longitudinal (u) and lateral (v) velocity components were measured. Therefore, the vertical and lateral turbulent pollution fluxes | All major flow (mean velocity and turbulence statistics, including momentum fluxes) and pollutant (mean and standard deviation of concentration) concentration qunatities, as well as turbulent and mean (advective) pollutant fluxes, were measured at the top (labelled T, Fig. 2c) and lateral (Fig. 2d) openings of the studied street canyon. Due to the uneven roof height, all quantities were measured at two heights in the case of the top openings. The first height was chosen at <i>z/H</i> = 0.6, which corresponds to the lowest street canyon wall (without taking roof pitches into account, see Fig. 2d). This height thus enclosed each street canyon of the non-uniform urban model from top. The second at <i>z/H</i> = 1 was chosen as the reference height for both urban models. In the case of the lateral openings, all quantitates were measured at the right (labelled R when viewed from downstream ) and left (labelled L) openings of each street canyon studied up to the height <i>z/H</i> = 0.6. At the top openings, the longitudinal (<i>u</i>u) and vertical (<i>w</i>) velocity components were measured simultaneously, while at the lateral openings, the longitudinal (<i>u</i>u) and lateral (<i>v</i>u) velocity components were measured. Therefore, the vertical and lateral turbulent pollution fluxes were measured for the upper and lateral openings, respectively. | ||
were measured for the upper and lateral openings, respectively. | |||
Revision as of 14:03, 9 May 2023
Pollutant transport between a street canyon and a 3D urban array as a function of wind direction and roof height non-uniformity
Description of Study Test Case
The following two figures show schematically the general set-up of the wind tunnel experiment and the cases investigated. In general, the urban model (either with even height, marked A1, or with uneven height, marked A2) was positioned in the middle of the wind tunnel test section (Fig. 1a). To simulate the oblique wind direction, the model was rotated 45 degrees in its centre (corresponding to the centre of the coordinates x,z,y). The first reference street canyon (hereafter called as A1-R) was part of the urban model A1, formed by evenly spaced 8 x 4 courtyard-type buildings of constant length (L = 300 mm, i.e. 120 m at full scale) and width (W = 150 mm, i.e. 60 m at full scale) and with pitched roofs of constant height H = 62.5 mm (i.e., 25 m at full scale and corresponds to the height of the roof ridges). The height of the eaves corresponded to z/H = 0.8. The second (A2-R) and third (A2-L) street canyons were part of the urban model A2 which had the same layout as the model A1 but had arbitrarily distributed roof heights (0.8H, H or 1.2H) along each building's wall (Fig. 2b). However, each of the non-uniform street canyons has the same mean height as that of the urban model with the constant roof height (H). Upstream of the model, a neutrally stratified atmospheric boundary layer was simulated using roughness elements and Irwin spires in the development section of the wind tunnel. Based on the mean height of the building (H) and the free flow velocity Uref = 6.2 ms-1 (which was used as the reference velocity), the flow was completely independent of the Reynolds number (i.e. ReB = HUref/ν = 24400, where ν is the kinematic viscosity of the air).
![](https://kbwiki-images.s3.amazonaws.com/thumb/a/aa/ExpSchema_tunel.jpg/740px-ExpSchema_tunel.jpg)
All major flow (mean velocity and turbulence statistics, including momentum fluxes) and pollutant (mean and standard deviation of concentration) concentration qunatities, as well as turbulent and mean (advective) pollutant fluxes, were measured at the top (labelled T, Fig. 2c) and lateral (Fig. 2d) openings of the studied street canyon. Due to the uneven roof height, all quantities were measured at two heights in the case of the top openings. The first height was chosen at z/H = 0.6, which corresponds to the lowest street canyon wall (without taking roof pitches into account, see Fig. 2d). This height thus enclosed each street canyon of the non-uniform urban model from top. The second at z/H = 1 was chosen as the reference height for both urban models. In the case of the lateral openings, all quantitates were measured at the right (labelled R when viewed from downstream ) and left (labelled L) openings of each street canyon studied up to the height z/H = 0.6. At the top openings, the longitudinal (uu) and vertical (w) velocity components were measured simultaneously, while at the lateral openings, the longitudinal (uu) and lateral (vu) velocity components were measured. Therefore, the vertical and lateral turbulent pollution fluxes were measured for the upper and lateral openings, respectively.
![](https://kbwiki-images.s3.amazonaws.com/thumb/3/3e/Schema.jpg/740px-Schema.jpg)
Contributed by: Štěpán Nosek — Institute of Thermomechanics of the CAS, v. v. i.
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