EXP 1-2 Description

Pollutant transport between a street canyon and a 3D urban array as a function of wind direction and roof height non-uniformity

Front Page

Introduction

Review of experimental studies

Description

Experimental Set Up

Measurement Quantities and Techniques

Data Quality and Accuracy

Measurement Data and Results

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 studied street canyons were positioned in the middle of the urban model (green rectangles in Fig. 2a and b), as well as the line source near the ground (the red line in Fig. 2a and b). For model A1, only the right street canyon (designated A1-R, viewed from downstream) was investigated due to symmetry, while the right (A2-R) and left (A2-L) street canyons were investigated in model A2 due to the uneven roof height. 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 $U_{ref}=6.2$ $ms^{-1}$ (which was used as the reference velocity), the flow was completely independent of the Reynolds number (i.e. $Re_{B}=HU_{ref}/\nu =24400$, where $\nu$ is the kinematic viscosity of the air).

Figure 1: Schematic representation of the experimental setup in the wind tunnel with reference to the wind tunnel coordinates (x,y,z). All dimensions are given in mm. Adapted from [1]

All major flow (mean velocity and turbulence statistics, including momentum fluxes) and pollutant (mean and standard deviation of concentration) concentrations, 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 were measured for the upper and lateral openings, respectively.

Figure 2: Schematic representation of the studied street canyons (green rectangles) in the city models with (a) uniform (with equal height H) and (b) non-uniform height. Measurement grid for the (c) top and the (d) lateral openings for all three investigated street canyons. The red line in (a) and (b) represents the near-ground line source, and the grey contours represent the dimensionless height z/H. Adapted from [2]

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Contributed by: Štěpán Nosek — Institute of Thermomechanics of the CAS, v. v. i.

Front Page

Introduction

Review of experimental studies

Description

Experimental Set Up

Measurement Quantities and Techniques

Data Quality and Accuracy

Measurement Data and Results

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