Turbulent Transfer Between Street Canyons and the Overlying Atmospheric Boundary Layer
Turbulent Transfer Between Street Canyons and the Overlying Atmospheric Boundary Layer
复制标题
街道峡谷和上覆大气边界层之间的湍流转移
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
R. Perkins
中科院分区：
文献类型：
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作者：
P. Salizzoni;M. Marro;L. Soulhac;N. Grosjean;R. Perkins
利用热线风速法和粒子图像测速法（PIV）对二维空腔与上覆边界层之间的湍流动量交换进行了实验研究。通过改变测试峡谷上游峡谷的宽度来改变边界层内的条件，同时保持测试峡谷的正方形几何形状。结果表明，湍流传递是由于峡谷上方剪切层产生的不稳定性与迎面层湍流结构之间的耦合所致。因此，没有一个单一的、独特的速度尺度可以正确地描述边界层上湍流动量交换所涉及的所有过程。同样，也没有单一的速度尺度可以表征峡谷内湍流的不同特性，这在很大程度上取决于外部流的湍流被带入空腔并被平均流携带的方式。在街道几何结构主要由相对较长的、均匀的网格状街道组成的情况下，本研究的结果将有助于为城市树冠中的动量交换开发简单的参数化；它们不太可能适用于由孤立的三维障碍物组成的稀疏几何。
The turbulent exchange of momentum between a two-dimensional cavity and the overlying boundary layer has been studied experimentally, using hot-wire anemometry and particle image velocimetry (PIV). Conditions within the boundary layer were varied by changing the width of the canyons upstream of the test canyon, whilst maintaining the square geometry of the test canyon. The results show that turbulent transfer is due to the coupling between the instabilities generated in the shear layer above the canyons and the turbulent structures in the oncoming boundary layer. As a result, there is no single, unique velocity scale that correctly characterizes all the processes involved in the turbulent exchange of momentum across the boundary layer. Similarly, there is no single velocity scale that can characterize the different properties of the turbulent flow within the canyon, which depends strongly on the way in which turbulence from the outer flow is entrained into the cavity and carried round by the mean flow. The results from this study will be useful in developing simple parametrizations for momentum exchange in the urban canopy, in situations where the street geometry consists principally of relatively long, uniform streets arranged in grid-like patterns; they are unlikely to be applicable to sparse geometries composed of isolated three-dimensional obstacles.