Physical Modeling of Flow Field inside Urban Street Canyons

Abstract

The flow characteristics inside urban street canyons were studied in a laboratory water channel. The approaching flow direction was horizontal and perpendicular to the street axis. The street width was adjusted to form street canyons of aspect ratios 0.5, 1.0, and 2.0. The velocity field and turbulent intensity were measured with a laser Doppler anemometer at various locations within the street canyons, which were used to elucidate the flow pattern inside the street canyons. It was found that the previous numerical modeling results are in good agreement with the current experimental results at most locations. For the street canyon of aspect ratio 0.5, which belongs to the wake interference flow regime, the mean and fluctuating velocity components were more difficult to measure as compared with the other two cases because of its more complicated flow pattern. Some guidelines for numerical modeling were developed based on the measurement results. The data presented in this paper can also be used as a comprehensive database for the validation of numerical models.

Large-Eddy Simulation of Flow and Pollutant Transports in and Above Two-Dimensional Idealized Street Canyons

“…5b). The current LES results are also compared with those of other LES (Liu et al 2004;Li et al 2008b) and a water-channel experiment (Li et al 2008a). The vertical profiles of the mean wind ( u and w ) and wind standard deviations (σ u and σ w ) are shown in Figs.…”

“…Owing to different domain heights in the studies (Table 1), U f is taken at different heights. The channel height in the water-channel experiment (Li et al 2008a) is 5h (= 0.5 m) and U f is taken at 3h. (Liu and Barth 2002) 0 .…”

“…In the wake interference regime (0.4 < h/b < 0.7), T increases with increasing aspect ratio that extends into the skimming flow regime (h/b > 0.7), and eventually peaks in the street canyon of aspect ratio between 0.6 and 0.8. Besides, Li et al (2008a) recently reported the mean and fluctuating velocities in street canyons of aspect ratio 0.5, 1 and 2 using water-channel experiments but pollutant dispersion was not included.…”

“…Cai et al (2008) examined the characteristic pollutant removal from street canyons of aspect ratio 1/3, 2/3, 1, 3/2 and 2 with line or area pollutant sources. Recently, Li et al (2008a) studied momentum and pollutant transport in deep street canyons of aspect ratio 3 and 5, which are commonly found in dense compact cities across the world. Apart from isothermal conditions, the number of large-eddy simulations investigating the effects of unstable stratification on the microscale climate in street canyons is increasing (Cai 2009;Li et al 2009Li et al , 2010Park and Baik 2009).…”

Experimental simulation of air quality in street canyon under changes of building orientation and aspect ratio

“…This shear may cause some sheltering effect on vertical turbulent transport across the canyon top, thereby suppressing pollutant removal from the canyon. 29 The profiles of longitudinal velocity that increased were directed upward starting from the half-height Z/H40.5. …”