Title: Multi-scale analysis of flow over heterogeneous urban enviornments Show Chinese title

Title: 多尺度流动分析在异质城市环境中的应用

Abstract: A multi-scale planar-averaging framework for urban areas is developed which enables efficient computation of coarse-grained quantities. We apply the multi-scale framework to a large-eddy simulation of an idealised heterogeneous urban environment of 512 buildings based on a typical London height distribution. We observe that for this geometry, the characteristic urban lengthscale l \approx 50 m, which is the averaging lengthscale L at which as much variance in the flow is resolved as is unresolved. For L>400 m, the statistics become approximately homogeneous, suggesting that non-building-resolving numerical weather prediction (NWP) models can be applied without modification at resolutions of 400 m and above for the case under consideration. We derive the multi-scale plane- and Reynolds-averaged momentum equation and show that for neutral cases, NWP models require parameterisation of the distributed drag and the unresolved turbulence and dispersive stress.We show that the universal drag parameterisation from Sutzl et al. 2020 (Bound-Layer Meteorol.178:225-248) holds reasonably well for resolutions L above 200 m. Below this value the problem becomes inhomogeneous and the parameterisation works less well. The unresolved stresses are well represented by a k-w closure with a value of w=0.4/s. However, an even more accurate closure can be derived from the Sutzl drag parameterisation that does not require further turbulence information. Show Chinese abstract

Abstract: 一种用于城市区域的多尺度平面平均框架被开发出来，该框架能够高效计算粗粒度量。 我们将多尺度框架应用于基于典型伦敦高度分布的理想化异质城市环境的大涡模拟，该环境包含512栋建筑。 我们观察到，在这种几何结构中，特征城市长度尺度 l \approx 50 米，这是平均长度尺度 L，在该尺度下流动中的方差被解析的部分与未被解析的部分相等。 对于 L>400 米，统计结果变得近似均匀，这表明在考虑的情况下，无需修改即可在 400 米及以上的分辨率下应用非建筑物解析数值天气预报（NWP）模型。 我们推导了多尺度平面平均和雷诺平均动量方程，并表明对于中性情况，NWP 模型需要对分布阻力和未解析湍流及分散应力进行参数化。我们表明，Sutzl 等人于 2020 年（Bound-Layer Meteorol. 178:225-248）提出的通用阻力参数化在分辨率 L 高于 200 米时表现良好。在此值以下，问题变得不均匀，参数化效果较差。 未解析应力可以通过 k-w 闭合来很好地表示，其中 w=0.4/s。 然而，可以从 Sutzl 阻力参数化中推导出一个更准确的闭合，而无需进一步的湍流信息。