High resolution urban large-eddy simulation studies from street canyon to neighbourhood scale
High resolution urban large-eddy simulation studies from street canyon to neighbourhood scale
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DOI：
10.1016/j.atmosenv.2008.08.001
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发表时间：
2008-12-01
影响因子：
5
通讯作者：
Raasch, Siegfried
中科院分区：
文献类型：
--
作者：
Letzel, Marcus Oliver;Krane, Martina;Raasch, Siegfried
在街道峡谷和街区尺度上研究了城市湍流特性。利用城市版本的并行LES模式PALM进行了三个高分辨率城市大涡模拟（LES）研究。验证结果表明，城市PALM模型的模拟结果与实验结果和大涡模拟结果一致，即上级优于快速廉价的传统RANS模型。首先是对峡谷内湍流特性和流动动力学的参数研究。主要结果如下：（1）深峡谷内积分垂直湍流廓线随峡谷宽度的变化规律。这与大尺度气象模式中的城市冠层参数化有关。(2)一个新的概念“空腔剪切层”补充经典的自由剪切层的概念。(3)首次在城市LES开尔文-亥姆霍兹不稳定性被确定在城市街道峡谷的顶部。这是相关的建模城市的分散，因为街道峡谷流通更间歇性比建议由以前的RANS results.Second，欧拉分散的情况下，研究表明，差异峡谷流动动力学反映在峡谷分散特性相比，以前的RANS研究。第三是一个邻里规模的城市LES可行性研究：被动示踪剂拉格朗日弥散动画新宿，东京市中心揭示湍流特征，上游流和不稳定性。其主要意义是始终使用三维模型进行湍流模拟，即使在准二维几何形状，不要低估湍流的不稳定性。对于垂直环境风，峡谷内速度分量的标准偏差不应视为常数，但可根据深峡谷中峡谷宽度的垂直比例方便地参数化。(c)2008爱思唯尔有限公司保留所有权利。
Urban turbulence characteristics are investigated at street canyon and neighbourhood scale. Three high resolution urban large-eddy simulation (LES) studies are performed using the urban version of the parallelized LES model PALM. Validation shows that the urban PALM version is in line with experimental and previous LES results, i.e. superior to the faster/cheaper conventional Reynolds-averaged (RANS) models.Two studies focus on quasi-2D urban street canyons driven by perpendicular flow. First is a parametric study of turbulence characteristics and flow dynamics within the canyon. The main results are: (1) Integral vertical turbulence profiles in deep canyons scale with canyon width. This is relevant for urban canopy parameterizations in larger-scale meteorological models. (2) A new concept of a "cavity shear layer" complements classical free shear layer concepts. (3) For the first time in urban LES Kelvin-Helmholtz instabilities are identified at the top of the urban street canyon. This is relevant for modelling urban dispersion, because the street canyon circulation is more intermittent than suggested by previous RANS results.Second, an Eulerian dispersion case study shows that differences in canyon flow dynamics are reflected in canyon dispersion characteristics compared to a previous RANS study. Third is a neighbourhood scale urban LES feasibility study: a passive tracer Lagrangian dispersion animation of Shinjuku, downtown Tokyo reveals turbulent flow features, upstream flow and intermittency. The main implications are always to use 3D models for turbulence simulations even in quasi-2D geometries, and not to underestimate the intermittency of turbulent flow. Standard deviations of velocity components within the canyon should not be treated as constant for perpendicular ambient wind but may be parameterized conveniently based on a vertical scaling with canyon width in deep canyons. (c) 2008 Elsevier Ltd. All rights reserved.