Spatial Characteristics of Roughness Sublayer Mean Flow and Turbulence Over a Realistic Urban Surface
Spatial Characteristics of Roughness Sublayer Mean Flow and Turbulence Over a Realistic Urban Surface
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DOI：
10.1007/s10546-016-0157-6
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发表时间：
2016-09-01
影响因子：
4.3
通讯作者：
Parlange, M. B.
中科院分区：
文献类型：
--
作者：
Giometto, M. G.;Christen, A.;Parlange, M. B.
来自城市塔楼的单点测量不能适当地量化湍流动能（TKE）预算中所有项的影响，并且通常不能代表整个城市领域的水平平均量。在这里进行了一系列大涡模拟（LES），以量化不可测量项的相关性，并探索瑞士巴塞尔市城市几何形状上和内部流场的空间变异性。该区域被选择在一个塔的中心，在那里可以在六个高度进行单点湍流测量。建筑物通过离散强迫浸入边界法表示，并基于测量数据集的详细真实几何形状。塔位置的局部模型结果与近中性稳定性条件下的测量结果以及为分析选择的两个盛行风向的测量结果比较良好。这证实了结合浸入边界条件的LES是研究真实城市粗糙度亚层湍流和弥散的一个有价值的模型。模拟结果证实，在RSL中平均速度分布的特征是一个拐点位于建筑物的平均高度之上。RSL中的TKE主要在上方产生，湍流向下输送到城市冠层。压力传递在极近壁区域是显著的。此外，时间平均变量和不可测量的色散项的空间变化在真实城市表面以上的RSL中很重要，因此在未来的城市冠层参数化发展中应予以考虑。
Single-point measurements from towers in cities cannot properly quantify the impact of all terms in the turbulent kinetic energy (TKE) budget and are often not representative of horizontally-averaged quantities over the entire urban domain. A series of large-eddy simulations (LES) is here performed to quantify the relevance of non-measurable terms, and to explore the spatial variability of the flow field over and within an urban geometry in the city of Basel, Switzerland. The domain has been chosen to be centered around a tower where single-point turbulence measurements at six heights are available. Buildings are represented through a discrete-forcing immersed boundary method and are based on detailed real geometries from a surveying dataset. The local model results at the tower location compare well against measurements under near-neutral stability conditions and for the two prevailing wind directions chosen for the analysis. This confirms that LES in conjunction with the immersed boundary condition is a valuable model to study turbulence and dispersion within a real urban roughness sublayer (RSL). The simulations confirm that mean velocity profiles in the RSL are characterized by an inflection point located above the average building height . TKE in the RSL is primarily produced above , and turbulence is transported down into the urban canopy layer. Pressure transport is found to be significant in the very-near-wall regions. Further, spatial variations of time-averaged variables and non-measurable dispersive terms are important in the RSL above a real urban surface and should therefore be considered in future urban canopy parametrization developments.