School of Environment and Architecture, University of Shanghai for Science and Technology, No.516, Jungong Road, Yangpu District, Shanghai, 200093, China.
Environ Sci Pollut Res Int. 2021 Mar;28(9):11618-11636. doi: 10.1007/s11356-020-11304-y. Epub 2020 Oct 30.
The thermal effect on the flow and dispersion of pollutants emitted from a rooftop stack is investigated by means of CFD (computational fluid dynamics) models with wind tunnel experimental validations. The leeward wall and its nearby ground are heated simultaneously to mimic solar radiation. Seventeen Ri (Richardson number) cases with four inflow wind speeds (1, 3, 6, and 9 m/s) and five temperature differences (0, 60, 120, 180, and 240 K) between the heated surface and ambient air are considered to represent the interaction between thermal buoyancy force and inertia force. The results reveal that (1) the steady RANS (Reynolds Averaged Navier-Stokes) computations with Boussinesq approximation can generally reproduce the effect of thermal buoyancy on the wake flow and pollutant distribution in wind tunnel experiments; (2) the wake vortex flow is less affected by the thermal buoyancy force at small Ri (e.g., Ri ≤ 0.26) while an upward flow rather than a clockwise vortex structure is developed in the near wake at Ri ≥ 0.58; (3) it is inappropriate to place fresh air intakes on the leeward wall of the emitting building, but natural ventilation through windows on the leeward wall can be implemented at higher Ri (e.g., Ri = 2.33); (4) at the pedestrian respiration height downstream of the building, the distance between the location of maximum pollutant concentration and the leeward wall increases linearly with Ri while the maximum dimensionless concentration decreases exponentially with increasing Ri; (5) the air temperature is rapidly reduced away from the heated wall/ground and a heat accumulation zone is formed at the ground corner next to the leeward wall. This study can be helpful for determining the strategy for natural ventilation through windows and for evaluating the impacts of rooftop stack exhaust on air quality downstream of emitting buildings.
通过带有风洞实验验证的计算流体动力学 (CFD) 模型研究了来自屋顶烟囱排放的污染物的流动和扩散的热效应。背风墙及其附近地面同时被加热以模拟太阳辐射。考虑了十七个 Ri（理查森数）案例，其中包括四个入流风速（1、3、6 和 9 m/s）和五个加热表面与环境空气之间的温差（0、60、120、180 和 240 K），以代表热浮力和惯性力之间的相互作用。结果表明：(1) 带有 Boussinesq 近似的稳态 RANS（雷诺平均纳维-斯托克斯）计算通常可以再现热浮力对风洞实验中尾流流动和污染物分布的影响；(2) 在小 Ri（例如，Ri≤0.26）下，尾流涡旋流动受热浮力的影响较小，而在近尾流中会形成向上的流动而不是顺时针涡旋结构在 Ri≥0.58 时；(3) 在排放建筑物的背风墙上不适合设置新鲜空气进气口，但在较高的 Ri（例如，Ri=2.33）下可以通过背风墙上的窗户实现自然通风；(4) 在建筑物下游的行人呼吸高度处，最大污染物浓度位置与背风墙之间的距离随 Ri 线性增加，而最大无量纲浓度随 Ri 的增加呈指数下降；(5) 空气温度从加热壁/地面迅速降低，并且在背风墙旁边的地面角落形成了一个热积累区。本研究有助于确定通过窗户进行自然通风的策略，并评估屋顶烟囱排放对排放建筑物下游空气质量的影响。
