Influence of thermal effect of building roof on pollutant diffusion under ideal conditions

Studies the influence of natural convection caused by the different roof thermal effect of the leeward building on the surrounding flow field, temperature field and the diffusion of gaseous pollutants emitted from the rooftop stack using CFD models coupled with the realizable K-ε turbulence model. Uses the Richardson number (Ri, from 0 to 1.15) to indicate the relative strength of the interaction between the thermal buoyancy force due to the heated building roof by solar radiation and the inertial force of the incoming flow. Verifies the numerical models by the wind tunnel experiments. The results show that there is a better agreement between the measured data by wind tunnel experiments and the predicted results by CFD models when the turbulent Schmidt number (Sct ) is 0.1. When Ri is less than 0.78, with the increase of Ri, the flow structure at the leeward side of the Building A changes significantly. The pollutant concentrations near the leeward wall of street canyon and on the pedestrian level plane are significantly reduced by 58% and 70%, respectively. Meanwhile, when Ri is greater than or equal to 0.78, compared with the inertial force, the thermal buoyancy force dominates, and the flow structure and pollutant distribution at the leeward side of the Building A basically do not change. In addition, due to the obvious uplift effect of thermal buoyancy, the concentration level of pollutants in street canyons is relatively low.