【摘要】 基于风洞实验验证的数值模型，探究大气稳定度（以整体理查森数Ri_b表征：-0.21～0.79）对下台阶式建筑屋顶烟囱污染物扩散分布的影响。结果表明，大气稳定度显著改变街谷内流场及污染物分布。稳定条件下（Ri_b > 0），街谷内垂直对流较弱：当Ri_b=0.43时，竖直中心面（y/H=0）无量纲速度差值（0.25）较中性条件减小13.80%;Ri_b=0.79时，人行呼吸高度面最大无量纲浓度（4.76）较中性条件升高18.70%。不稳定条件下（Ri_b<0），街谷内垂直对流增强，近地面风速增大，污染物浓度明显降低：当Ri_b=-0.19时，竖直中心面无量纲速度差值（0.32）较中性条件升高10.34%;Ri_b=-0.21时，人行呼吸高度面最大无量纲浓度（0.88）较中性条件降低78.19%。本研究揭示了不同大气稳定度下城市局部流场与污染物的扩散规律，为针对性改善空气质量提供理论基础。更多还原

【Abstract】 Based on a numerical model validated by wind tunnel experiments, the influence of atmospheric stability, characterized by the bulk Richardson number(Ri_b) in the range of-0.21 to 0.79,on the diffusion of pollutants from roof chimneys on step-down buildings was investigated. The results indicate that the flow field and pollutant distribution within the street canyon are significantly altered by atmospheric stability. Under stable conditions(Ri_b > 0), vertical convection within the street canyon was weak. At Ri_b = 0.43, the dimensionless velocity difference(0.25) on the vertical center plane(y/H = 0)was reduced by 13.80% compared to that under neutral conditions. At Ri_b = 0.79, the maximum dimensionless concentration(4.76) at the pedestrian breathing level was increased by 18.70%. Under unstable conditions(Ri_b < 0), vertical convection was enhanced, with increased wind speed near the ground, leading to a notable decrease in pollutant concentration. At Ri_b =-0.19, the dimensionless velocity difference(0.32) on the vertical center plane was increased by 10.34%. At Ri_b =-0.21, the maximum dimensionless concentration(0.88) at the pedestrian breathing level was decreased by78.19%. The patterns of local urban flow fields and pollutant dispersion under different atmospheric stability conditions are revealed, providing a theoretical basis for targeted air quality improvement.更多还原