Abstract/Summary

Deep street canyons and unfavourable meteorological conditions usually induce high pollutant exposure. Validated by experimental data, this paper employs computational fluid dynamic simulations with RNG k-ε model to investigate the flow, and passive pollutant dispersion within scale-model two-dimensional street canyons(H=3m). As a novelty, this paper quantifies the impacts of various wall heating scenarios(bottom, leeward/windward wall and all-wall heating), ambient velocity(Uref=0.5-2m/s, Froude numbers Fr=0.25-4.08, Reynolds numbers Re=95602-382409) and aspect ratios(building height/street width, AR=0.5, 0.67, 1, 2, 3) on personal intake fraction for entire streets(<P_IF>). The governing equations are implicitly discretized by a finite volume method (FVM) and the second-order upwind scheme with Boussinesq model for quantifying buoyancy effects. The SIMPLE scheme is adopted for the pressure and velocity coupling. In most isothermal cases, one-main-vortex structure exists as AR=0.5-3(<P_IF>=0.43-3.96ppm and 1.66-27.51ppm with Uref=2 and 0.5m/s). For non-isothermal cases with Fr=4.08(Uref=2m/s), wind-driven force dominates urban airflow as AR=0.5-1 and four heating conditions attain similar <P_IF>(0.39-0.43ppm, 0.57-0.60ppm, 0.91-0.98ppm). As AR=2, windward and all-wall heating get two-vortex structures with greater <P_IF>(3.18-3.33ppm) than others(<P_IF>=2.13-2.21ppm). As AR=3, leeward-wall heating slightly reduces <P_IF>(∼3.72-3.96ppm), but the other three produce two-vortex structures with greater <P_IF>(6.13-10.32ppm). As Fr=0.25(Uref=0.5m/s), leeward-wall heating always attains smaller <P_IF>(1.20-7.10ppm) than isothermal cases(1.66-27.51ppm) as AR=0.5-3, however the influence of the other three is complicated which sometimes raises or reduces <P_IF>. Overall, smaller background wind speed (Fr=0.25) with two-vortex structures attains much larger <P_IF>. Special attention is required at night(all-wall heating), noon(bottom-heating) and cloudy period(no-wall heating) as AR=2-3, while it is during windward-wall heating and cloudy period for AR=0.5-1.