EXP 1-2 Measurement Data and Results: Difference between revisions
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<math>\frac{\overline{c^{*}w}}{U_{ref}} = \frac{\overline{\frac{cU_{ref}HLw}{Q}}}{U_{ref}} = \frac{HL}{Q}\overline{cw}</math>, (1) | <math>\frac{\overline{c^{*}w}}{U_{ref}} = \frac{\overline{\frac{cU_{ref}HLw}{Q}}}{U_{ref}} = \frac{HL}{Q}\overline{cw}</math>, (1) | ||
where <i>c<sup>*< | where <i>c<sup>*</sup></i> is the instantaneous dimensionless concentration, c is the instantaneous concentration, w is the instantaneous vertical velocity component, Uref is the reference velocity (here the freestream velocity), H is the reference height (here the height of the building of uniform roofs), L is the length of the line source, Q is the volumetric flow of ethane from the line source, and the overbar denotes the time averaging. Similarly, the mean dimensionless total latera pollution fluxes were calculated for the lateral opening as | ||
<math>\frac{\overline{c^{*}v}}{U_{ref}} = \frac{\overline{\frac{cU_{ref}HLv}{Q}}}{U_{ref}} = \frac{HL}{Q}\overline{cv}</math>, (2) | <math>\frac{\overline{c^{*}v}}{U_{ref}} = \frac{\overline{\frac{cU_{ref}HLv}{Q}}}{U_{ref}} = \frac{HL}{Q}\overline{cv}</math>, (2) | ||
Revision as of 11:44, 11 May 2023
Pollutant transport between a street canyon and a 3D urban array as a function of wind direction and roof height non-uniformity
Measurement data/results
Figs. 1 and 2 show the mean dimensionless total pollution fluxes through the top (at z/H = 0.6) and side openings of the studied street canyons for the vertical (90°) and oblique (45°) wind directions, respectively. The mean dimensionless total vertical pollution fluxes were calculated for the top opening as
, (1)
where c* is the instantaneous dimensionless concentration, c is the instantaneous concentration, w is the instantaneous vertical velocity component, Uref is the reference velocity (here the freestream velocity), H is the reference height (here the height of the building of uniform roofs), L is the length of the line source, Q is the volumetric flow of ethane from the line source, and the overbar denotes the time averaging. Similarly, the mean dimensionless total latera pollution fluxes were calculated for the lateral opening as
, (2)
where v is the lateral velocity component.
Fig. 1a shows that in the case of the uniform roof, the pollutant is transported up the leeward wall and down the windward wall due to the vertical recirculation in the middle of the street canyon. Near the lateral ends of the street canyon, the pollutant is transported by horizontal recirculation, also known as corner vortex. This type of transport can also be observed at the lateral openings of the street canyon. However, in the case of the uneven roof heights, these vortices are either absent altogether, as in the case of the right uneven street canyon (Fig. 1b), or they are enhanced, as in the case of the left uneven canyon (Fig. 1c). Especially near the right lateral end (seen from the downstream) of the left non-uniform canyon, there is a very strong horizontal recirculation that traps the pollutant also at the windward wall (se y= 1H in Fig. 1c). It can also be seen from Fig. 1 that both the uniform and left non-uniform street canyons have a higher re-emission (negative total pollutant flux) of the pollutant than the right non-uniform canyon and are therefore more poorly ventilated.
Contributed by: Štěpán Nosek — Institute of Thermomechanics of the CAS, v. v. i.
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