Abstract The Reynolds independence has been important for scaled experiments of urban aerodynamics in wind environment engineering. It helps to circumvent the difficulty in conserving the Re number for large scaling ratios. However, the criteria for Re-independence and its working mechanism have not been well investigated quantitatively. In this study, a dimensionless numerical analysis is conducted to provide a microscopic view of the problem both theoretically and numerically. The conditions of the similarity and Re-independence are identified theoretically. A series of simulations of the typical urban canopy layer model with three typical building-street aspect ratios were performed to quantify the similarity levels by some new evaluation metrics, local adapted deviation rate (ADR), the turbulence viscosity ratio (TVR), and the fraction of laminar viscosity ( μ ’ / μ e f f ’ ). It is found that one explanation for the similarity of Re-independence is that either the convection of the flow dominates the diffusion, and/or the turbulence viscosity dominates the laminar viscosity inside the diffusion term. A regional critical Re number ( R e c r − r ) concept is introduced to describe the case-specific and region-specific Re-independence: it is around 10,000–30,000 for the canyon and building height regions, and 60,000–140,000 for the near-wall regions.

中文翻译：

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城市空气动力学雷诺独立性和区域临界雷诺数的量纲分析

摘要 雷诺独立性对于风环境工程中城市空气动力学的规模化实验具有重要意义。它有助于规避在大缩放比例下保存 Re 数的困难。然而，重新独立的标准及其工作机制尚未得到很好的定量研究。在这项研究中，进行了无量纲数值分析，以从理论上和数值上提供问题的微观视图。理论上确定了相似性和重新独立性的条件。对具有三种典型建筑-街道纵横比的典型城市冠层模型进行了一系列模拟，通过一些新的评估指标、局部适应偏差率 (ADR)、湍流粘度比 (TVR)、和层流粘度的分数（ μ ' / μ eff ' ）。发现重新独立性的相似性的一种解释是流动的对流支配扩散，和/或湍流粘度支配扩散项内的层流粘度。引入了区域临界 Re 数 (R ecr − r ) 概念来描述特定案例和特定区域的重新独立性：峡谷和建筑物高度区域约为 10,000-30,000，近壁区域。