We describe and explain the turbulent processes at play in the lower part of the urban boundary layer through performing a large-eddy simulation of the flow over an urban-like canopy composed of a staggered array of cubes with a packing density of 25%. The simulation models neutral thermal conditions at a Reynolds number (based on both velocity at the top of the domain and the domain height) of Re=50,000\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Re = 50{,}000$$\end{document}. A dynamic Smagorinsky model is implemented in order to allow for energy backscattering from subgrid scales. A wall refinement of the grid allows resolving the viscous sublayer. Turbulent statistics up to the third order, as well as each term of the turbulence-kinetic-energy budget, are computed individually everywhere in the domain. Results are discussed in relation to experimental and numerical data from the literature in order to describe turbulent energy transfers occurring in the roughness sublayer. The fine grid resolution close to surfaces serves to analyze in depth the three-dimensional distribution of turbulence production inside the urban canopy layer. This analysis in turn leads to discovering areas, never previously documented in an urban-like canopy, of highly positive and highly negative production close to the surface, away from the well-known high production area in the shear layer. Furthermore, evidence of a close link between high and low production areas near the surfaces and singular points in the mean flow is presented, thus laying the groundwork for a simple pre-diagnostic tool to detect turbulence-kinetic-energy production areas near surfaces.

中文翻译：

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使用大涡模拟的类似城市边界层的湍流动能收支

我们通过对由交错排列的立方体组成的城市冠层的流动进行大涡模拟来描述和解释在城市边界层下部起作用的湍流过程，其堆积密度为 25%。模拟以 Re=50,000\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage 的雷诺数（基于域顶部的速度和域高度）模拟中性热条件{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Re = 50{,}000$$\结束{文档}。实现了动态 Smagorinsky 模型，以允许来自子网格尺度的能量反向散射。网格的壁细化允许解析粘性子层。高达三阶的湍流统计数据以及湍流-动能预算的每一项都在域中的任何地方单独计算。结果结合文献中的实验和数值数据进行了讨论，以描述粗糙度子层中发生的湍流能量转移。靠近表面的精细网格分辨率用于深入分析城市冠层内湍流产生的三维分布。这种分析反过来又导致发现区域，以前从未在类似城市的树冠中记录过，靠近地表的高度正和高度负的产量，远离剪切层中众所周知的高产量区域。此外，