Wake Characteristics of Tall Buildings in a Realistic Urban Canopy
Wake Characteristics of Tall Buildings in a Realistic Urban Canopy
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DOI：
10.1007/s10546-019-00450-7
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发表时间：
2019-08-01
影响因子：
4.3
通讯作者：
Hayden, Paul
中科院分区：
文献类型：
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作者：
Hertwig, Denise;Gough, Hannah L.;Hayden, Paul
城市中高楼大厦的存在会影响城市树冠内部和上方的动量和标量交换。由于尾流效应在很长的距离上可能是重要的，它们对于在不同空间尺度上和跨空间尺度的城市流建模至关重要。我们探讨了高层建筑在微观和局部尺度上的空气动力学效应，重点是在伦敦市中心现实的城市环境中，尾流结构、树冠和周围粗糙度次层流之间的相互作用。边界层风洞的流动实验采用1：200的模型，两个高楼(81m和134.3m)各有两个风向。当高楼大厦是复杂的城市树冠的一部分而不是孤立的时，尾流的平均流动、湍流统计和瞬时流动结构的巨大变化是明显的。在近尾迹中，较低建筑物的存在使回流区的核心向上移动，从而减少了发生气流逆转的垂直深度。这放大了屋顶的垂直切变，增强了湍流动量交换。在主尾迹的近端，横向速度脉动和湍流动能比孤立的建筑物情况要小，因为在城市冠层和粗糙度下层中产生的涡旋将能量向下分配到更小的尺度上，从而更快地消散。对孤立建筑物绕流的尾流模型的评估表明，需要对模型进行改进，以解释高层建筑顶棚中的这种流动结构变化。
The presence of tall buildings in cities affects momentum and scalar exchange within and above the urban canopy. As wake effects can be important over large distances, they are crucial for urban-flow modelling on and across different spatial scales. We explore the aerodynamic effects of tall buildings on the microscale to local scales with a focus on the interaction between the wake structure, canopy and roughness sublayer flow of the surroundings in a realistic urban setting in central London. Flow experiments in a boundary-layer wind tunnel use a 1:200 scale model with two tall buildings (81m and 134.3m) for two wind directions. Large changes in mean flow, turbulence statistics and instantaneous flow structure of the wake are evident when tall buildings are part of the complex urban canopy rather than isolated. In the near-wake, the presence of lower buildings displaces the core of the recirculation zone upwards, thereby reducing the vertical depth over which flow reversal occurs. This amplifies vertical shear at the rooftop and enhances turbulent momentum exchange. In the near part of the main wake, lateral velocity fluctuations and hence turbulence kinetic energy are reduced compared to the isolated building case as eddies generated in the urban canopy and roughness sublayer distribute energy down to smaller scales that dissipate more rapidly. Evaluation of a wake model for flow past isolated buildings suggests model refinements are needed to account for such flow-structure changes in tall-building canopies.