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Dispersive Fluxes Within and Over a Real Urban Canopy: A Large-Eddy Simulation Study
Boundary-Layer Meteorology ( IF 4.3 ) Pub Date : 2022-08-02 , DOI: 10.1007/s10546-022-00725-6
Emmanuel Akinlabi, Björn Maronga, Marco G. Giometto, Dan Li

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.



中文翻译:

真实城市树冠内部和之上的色散通量:大涡模拟研究

大涡模拟 (LES) 用于研究美国波士顿市真实城市树冠内部和之上的动量和被动标量的传输。这种城市天篷的特点是复杂的建筑布局、密度和方向,高层建筑。特别关注色散动量和标量通量的大小、可变性和结构,以及它们对湍流动量和标量通量的相对重要性。我们首先通过将模拟城市冠层上的流量统计数据与先前研究中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,我们观察到分散动量和标量通量可能超过平均建筑高度的 2-5 倍,这是城市粗糙度子层高度的常用定义。在平均建筑物高度之上,色散通量变得弱依赖于网格间距,色散动量通量对湍流和色散动量通量总和的贡献约为 10-15%,并且不会随着高度的增加而单调减少。色散动量和标量通量对时间和空间平均很敏感。我们进一步发现,分散通量的成分在空间上是异质的,并因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型中对真实城市檐篷上的湍流和分散通量进行参数化。分散动量通量对湍流和分散动量通量总和的贡献约为 10-15%,并且不会随着高度的增加而单调减少。色散动量和标量通量对时间和空间平均很敏感。我们进一步发现,分散通量的成分在空间上是异质的,并因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型中对真实城市檐篷上的湍流和分散通量进行参数化。分散动量通量对湍流和分散动量通量总和的贡献约为 10-15%,并且不会随着高度的增加而单调减少。色散动量和标量通量对时间和空间平均很敏感。我们进一步发现,分散通量的成分在空间上是异质的,并因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型中对真实城市檐篷上的湍流和分散通量进行参数化。

更新日期:2022-08-03
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