Side ratio effects on flow and pollutant dispersion around an isolated high-rise building in a turbulent boundary layer

Abstract

Large-eddy simulations were performed to investigate side ratio (SR) effects on flow and dispersion around an isolated high-rise building. Four cross sections were considered with SR ranging from 0.25 to 1.5. Three pollutants were released from the ground; the first source (P1) was upwind of the building, and the other two (P2 and P3) were downwind. Reattachments on the side and top surfaces were observed for SR = 1.5. As SR decreased, the recirculation area behind the building increased and vortex shedding strengthened. The dispersion area of pollutant P1 nearly coincided with the primary separation region at ground level because its source location was inside the primary separation region. More of pollutant P2 accumulated near the leeward wall because the discharge hole was located inside the recirculation region behind the building for all simulations, and large SR values had high P2 concentrations because of the weak vortex shedding strength. Pollutant P3 (whose source was far from the building) exhibited different distribution patterns because of different recirculation sizes; it was blown directly downstream for SR = 1.5 and 1.0, whereas more was transported back toward the leeward wall for SR = 0.25. An analysis of the probability density functions of instantaneous concentration indicated that positive fluctuations of the concentration occurred more frequently near source locations; the opposite held in relatively low-concentration areas. The extremely high positive fluctuations reached 15 times the standard deviation for the second mode.