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Effect of hilly urban morphology on dispersion in the urban boundary layer

机译:丘陵城市形态对城市边界层扩散的影响

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Air flow and dispersion in the atmospheric surface layer are strongly affected by terrain and buildings. Through Large-eddy simulation (LES) with a three-dimensional immersed boundary method (IBM) atmospheric boundary layer flow in a hilly urban area was simulated to study turbulence and dispersion properties in and above the urban canopy. Five different domains were designed to simulate flow over an infinite sequence of hills (defined by the Witch of Agnesi and having a maximum slope of 0.26), buildings on flat terrain and buildings on the Witch of Agnesi hills (hill height to building height ratios 3/2 and 9/ 4). Shear stress and velocity variance above the urban canopy were smaller for the small hill with buildings compared to building array on flat terrain. Shear stress increased with the hill height for hills with buildings. For hills with buildings turbulence kinetic energy (TKE) in the urban canopy increased dramatically upwind of the hillcrest and fell below the canopy level TKE for the flat urban case in the lee of the hill. Canyon ventilation at the sub-canopy level was two to three times larger for the hilly urban case compared to the flat case, but air exchange through the top of urban canyons was not greatly affected by the hill. Our study demonstrates that urban dispersion models with the ability to handle terrain and bluff obstacles in the domain are necessary to simulate important flow features and dispersion in hilly urban environments.
机译:地形和建筑物强烈影响大气表层中的气流和扩散。通过三维沉浸边界法(IBM)的大涡模拟(LES),模拟了丘陵市区大气边界层的流动,以研究城市冠层内外的湍流和弥散特性。设计了五个不同的域来模拟无限序列的山丘上的流量(由Agnesi女巫定义,最大坡度为0.26),平坦地形上的建筑物以及Agnesi Witch上的建筑物(山高与建筑物高度之比3 / 2和9/4)。与平坦地形上的建筑物阵列相比,带有建筑物的小山丘的城市冠层上方的剪应力和速度方差较小。带有建筑物的山丘的剪应力随山丘高度的增加而增加。对于具有建筑物的山丘,城市冠层中的湍流动能(TKE)急剧增加,在山顶上的平坦城市案例中,山顶的上风向后降到了冠层水平TKE以下。与平坦的情况相比,丘陵城市案例的亚冠层峡谷通风量要大2到3倍,但是通过城市峡谷顶部的空气交换不受丘陵影响很大。我们的研究表明,具有模拟地形和虚张声势障碍能力的城市分散模型对于模拟丘陵城市环境中的重要流量特征和分散是必不可少的。

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