Dispersive Fluxes Within and Over a Real Urban Canopy: A Large-Eddy Simulation Study
Dispersive Fluxes Within and Over a Real Urban Canopy: A Large-Eddy Simulation Study
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DOI：
10.1007/s10546-022-00725-6
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发表时间：
2022-08
影响因子：
4.3
通讯作者：
Emmanuel O. Akinlabi;B. Maronga;M. Giometto;Dan Li
中科院分区：
文献类型：
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作者：
Emmanuel O. Akinlabi;B. Maronga;M. Giometto;Dan Li
采用大涡模拟（LES）方法研究了美国波士顿城市林冠内部和林冠上空动量和被动标量的输运。这个城市天篷的特点是复杂的建筑布局、密度和朝向与高层建筑。特别注意色散动量和标量通量的大小、变异性和结构，以及它们与湍流动量和标量通量的相对重要性。我们首先通过将模拟的城市冠层上的流量统计数据与先前研究报告的数据进行比较来评估LES模型。在考虑的真实城市冠层的模拟中，我们观察到色散动量和标量通量在平均建筑高度的2-5倍以上可能很重要，这是城市粗糙度子层高度的常用定义。在平均建筑高度以上，色散动量通量对栅格间距的依赖性较弱，色散动量通量对湍流和色散动量通量的贡献约为10-15%，并且不随高度的增加而单调减小。色散动量和标量通量对时间和空间平均都很敏感。我们进一步发现，色散通量的组成在空间上是异质的，并且由于高层建筑的存在而增强。这项工作表明，需要在中尺度和大尺度模式中参数化真实城市冠层上的湍流和弥散通量。
Large-eddy simulations (LES) are conducted to study the transport of momentum and passive scalar within and over a real urban canopy in the City of Boston, USA. This urban canopy is characterized by complex building layouts, densities and orientations with high-rise buildings. Special attention is given to the magnitude, variability and structure of dispersive momentum and scalar fluxes and their relative importance to turbulent momentum and scalar fluxes. We first evaluate the LES model by comparing the simulated flow statistics over an urban-like canopy to data reported in previous studies. In simulations over the considered real urban canopy, we observe that the dispersive momentum and scalar fluxes can be important beyond 2–5 times the mean building height, which is a commonly used definition for the urban roughness sublayer height. Above the mean building height where the dispersive fluxes become weakly dependent on the grid spacing, the dispersive momentum flux contributes about 10–15% to the sum of turbulent and dispersive momentum fluxes and does not decrease monotonically with increasing height. The dispersive momentum and scalar fluxes are sensitive to the time and spatial averaging. We further find that the constituents of dispersive fluxes are spatially heterogeneous and enhanced by the presence of high-rise buildings. This work suggests the need to parameterize both turbulent and dispersive fluxes over real urban canopies in mesoscale and large-scale models.