Belcher Stephen E
University of Reading Department of Meteorology Early Gate, PO Box 243, Reading RG6 6BB, UK.
Philos Trans A Math Phys Eng Sci. 2005 Dec 15;363(1837):2947-68. doi: 10.1098/rsta.2005.1673.
Concern over terrorist releases of harmful material has generated interest in short-range air-borne dispersion in urban areas. Here, we review the important fluid dynamical processes that control dispersion in the first kilometre, the neighbourhood scale, when much of the material remains within the urban canopy. Dispersion is then controlled by turbulent mixing and mean flow transport through the network of streets. We consider mixing and transport in a long straight street, street intersections and then a network of streets connected by intersections. The mixing and transport in these systems are illustrated with results from recent fine-resolution numerical simulations and laboratory models, which then inform simpler scaling estimates and modelling schemes. Finally, we make some tentative steps to pull the process studies together to begin to understand results from full-scale observations. In particular, it is shown that the positions of 'shear layers' and 'dividing streamlines' largely control the patterns of mixing and transport. It is also shown that neighbourhood-scale dispersion follows one scaling in the near field and another in the far field after passage through many intersections. The challenge for the future is to bring these threads together into a coherent mathematical model.
对恐怖分子释放有害物质的担忧引发了人们对城市地区短程空气传播扩散的兴趣。在此，我们回顾了在物质大部分仍处于城市冠层内的邻里尺度下，控制首公里扩散的重要流体动力学过程。此时，扩散由湍流混合以及通过街道网络的平均流输运所控制。我们考虑在一条长直街道、街道交叉口以及由交叉口相连的街道网络中的混合与输运。这些系统中的混合与输运通过近期高分辨率数值模拟和实验室模型的结果进行说明，进而为更简单的尺度估计和建模方案提供依据。最后，我们采取一些初步措施将过程研究整合起来，以开始理解全尺度观测的结果。特别指出的是，“剪切层”和“分流线”的位置在很大程度上控制着混合与输运模式。还表明，邻里尺度的扩散在经过多个交叉口后，在近场遵循一种尺度规律，在远场遵循另一种尺度规律。未来的挑战是将这些线索整合到一个连贯的数学模型中。
