Large Eddy Simulation Model for Complex Urban Surfaces and the Implication to Surface Similarity Law

复杂城市地表大涡模拟模型及其对地表相似律的影响

• 批准号: 15360262
• 负责人: KANDA Manabu
• 金额: $ 5.89万
• 依托单位: Tokyo Institute of Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2003
• 资助国家: 日本
• 起止时间: 2003 至 2004
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15360262/
• 关键词: LES; Urban Boundary Layer; Atmospheric Boundary Layer; Turbulent Organized Structures; Urban Canopy; Tower; Scale model; Urban Meteorology; 都市の大気; ストリートキャニオン; 住宅群

Large Eddy Simulations have been performed for fully developed turbulent flow within and above explicitly resolved simple cubic arrays. The model (LES-CITY) was validated in comparison with laboratory experiments. The systematic influence of cubic density on turbulent flow characteristics was investigated through numerical experiments in a wide range of cubic area density (0 % to 44%). The following results were obtained, (1)The influence of the heterogeneity of surface geometry : the dispersive momentum flux is quite large within the canopy layer due to a mean stream such as re-circulation, while it is small but not negligible above the canopy due to Turbulent Organized Structures(TOS). The spatial variation of temporally averaged momentum in the roughness sub-layer is as large as 10-20 % of the total kinematic surface drag. (2)The intermittency of flow : the temporally and spatial-ensemble averaged flow structure confirm the existence of conventionally described canyon flow regimes ; … More isolated, interfacial and wake. However, the intermittency of the canyon flow for any cubic densities is quite large and the stream patterns are never persistent. (3)TOS : TOS similar to those observed in turbulent surface layer flows are simulated, which are characterized by longitudinally-elongated low speed streaks and the corresponding shorter stream wise vortices. The streaks in sparse and dense canopy flows are likely to be aligned to the street-line and to the roof-lines, respectively. Such heterogeneity of TOS partially accounts for the large spatial variation of momentum flux. (4)The difference from vegetation flow : the TOS and the resulting turbulent statistics of urban flow above the canopy resemble those in surface layers, contrast to the mixing layer analogy of vegetation flows. The re-circulation within the canopy makes significant influence on the turbulent statistics such as negative Reynolds stress, large dispersive flux and standard deviations, and the up-shift of the displacement height.Turbulent organized structures above building arrays were investigated using a large eddy simulation(LES) model for a city (LES-CTTY). Square and staggered building arrays produced contrasting behavior in terms of turbulence that roughly corresponded to the conventional classification of ‘D-type' and ‘K-type' roughness, respectively, (1)The drag coefficients at the building heights for staggered arrays were sensitive to building area density, but those for square arrays were not (2)The relative contributions of ejections to sweeps ( ) at the building height for square arrays were sensitive to building area density and nearly equaled or exceeded 1.0(ejection dominant), but those for staggered arrays were insensitive to building area density and were mostly below 1.0(sweep dominant). (3)Streaky patterns of longitudinal low speed regions (i.e., low speed streaks) existed in all flows regardless of array type. Height variations of the buildings in the square array drastically increased the drag coefficient and modified the turbulent flow structures. The mechanism of D-type and K-type urban-like roughness flows and the difference from vegetation flows are discussed. Although urban-like roughness flows exhibited mixed properties of mixing layers and flat-wall boundary layers as far as was concerned, the turbulent organized structures of urban-like roughness flows resembled those of flat-wall boundary layers. Less

对于显式解析的简单三次阵列内部和上方的充分发展的湍流，已经进行了大涡模拟。模型(LES-CITY)与实验室实验结果进行了对比验证。通过数值实验，在较宽的立方体面积密度范围内(0%~44%)，研究了立方体密度对湍流流动特性的系统影响。结果表明：(1)地表几何形状非均质性的影响：由于环流等平均流的影响，冠层内的弥散动量通量很大，而由于湍流组织结构(TOS)，冠层以上的动量通量很小，但不可忽略。粗糙度子层的时间平均动量在空间上的变化可达总运动表面阻力的10-20%。(2)流动的间歇性：时间和空间集合的平均流动结构证实了传统上描述的峡谷流态的存在；…更与世隔绝、相互联系和觉醒。然而，对于任何立方体密度，峡谷流的间歇性都是相当大的，并且溪流模式从来不是持续的。(3)模拟了TOS：TOS：模拟的TOS与湍流表面层中观察到的TOS相似，其特征是纵向拉长的低速条纹和相应的较短的流向涡。稀疏和密集的树冠流中的条纹可能分别与街道线和屋顶线对齐。TOS的这种非均质性部分解释了动量通量的较大空间变化。(4)与植被流的不同之处：与植被流的混合层相似，冠层以上城市流的TOS和由此产生的湍流统计与近地面层相似。冠层内再环流对雷诺应力为负值、弥散通量和标准差较大、位移高度上移等湍流统计特性有显著影响，利用大涡模拟(LES-CTTY)模式研究了建筑物阵列上方的湍流组织结构。正方形和交错排列的建筑物在湍流方面产生了不同的行为，大致对应于传统的D型和K型粗糙度分类，(1)交错排列的建筑物高度处的阻力系数对建筑物面积密度敏感，而正方形排列的阻力系数对建筑物高度的扫掠()相对贡献()正方形排列对建筑物高度的扫掠很敏感，几乎等于或超过1.0(抛射为主)，但交错排列的阻力系数对建筑物面积密度不敏感，大多低于1.0(扫掠为主)。(3)无论阵列类型如何，在所有流动中都存在纵向低速区(即低速条纹)的条纹图案。方形阵列中建筑物高度的变化使阻力系数显著增加，并改变了湍流结构。讨论了D型和K型城市粗糙度流的形成机制及其与植被流的区别。尽管城市状粗糙流表现出混合层和平壁边界层的混合特性，但城市状粗糙流的湍流组织结构与平壁边界层相似。较少

项目成果

The impact of the surface heterogeneity on the energy imbalance.

表面异质性对能量不平衡的影响。

• 发表时间: 2005
• 期刊: Annual J.of Hydraulic Eng., JSCE Vol.49
• 作者: A.Inagaki;M.Kanda;M.O.Letzel;S.Raasch
• 通讯作者: S.Raasch

Large eddy simulation of turbulent organized structure within and above explicitly resolved cubic arrays.

对显式解析的立方阵列内部和上方的湍流组织结构进行大涡模拟。

• 发表时间: 2004
• 期刊: Boundary-Layer Meteorology 112
• 作者: M.Kanda;R.Moriwaki;F.Kasamatsu
• 通讯作者: F.Kasamatsu

A simple 3-dimensional urban energy balance model and outdoor.

一个简单的 3 维城市能量平衡模型和室外。

• 发表时间: 2005
• 期刊: Annual J.of Hydraulic Eng., JSCE Vol.49
• 作者: T.Kawai;M.Kanega;M.Kanda
• 通讯作者: M.Kanda

Potential temperature profiles in and above an urban canopy based on a long-term field measurement.

基于长期现场测量的城市冠层内部和上方的潜在温度剖面。

• 发表时间: 2004
• 期刊: Annual J.of Hydraulic Eng., JSCE Vol.48
• 作者: Y.Kimoto;R.Moriwaki;M.Kanda
• 通讯作者: M.Kanda

Shear functions of wind and temperature in an urban surface layer.

城市表层风和温度的切变函数。

• 发表时间: 2004
• 期刊: Annual J.of Hydraulic Eng., JSCE Vol.48
• 作者: R.Moriwaki;M.Kanda;Y.Kimoto
• 通讯作者: Y.Kimoto