Impacts of urban morphometric indices on ventilation
Impacts of urban morphometric indices on ventilation
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DOI：
10.1016/j.buildenv.2022.109907
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发表时间：
2022-12
影响因子：
7.4
通讯作者：
G. Duan;K. Nakamae;T. Takemi
中科院分区：
文献类型：
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作者：
G. Duan;K. Nakamae;T. Takemi
通风对城市几何异质性表现出很强的敏感性;然而，与城市形态指标的定量联系，如堆积密度（分别为前沿和平面区域的λ f和λ p）和建筑物高度变异性（σ H），仍然不清楚。采用大涡模拟方法，研究了真实的城市区域湍流边界层中污染物标量的扩散。虽然区域平均浓度的时间历程在所有情况下都遵循熟悉的指数衰减函数，但衰减速率不同，并且对λ f有明显的单调依赖性。平均示踪剂年龄τ a与λ f也呈现出很强的线性标度关系（R2 = 0. 8）;然而，通气时间尺度与其他形态学指标（如λ p和σ H）之间的明确关系很难辨别。一个有效的峡谷的长宽比（A R eff）提出了真实的城市地区，它允许通风量化在一个简单的方式为理想的峡谷。年龄谱测量了多个时间尺度上示踪剂年龄的概率密度函数，分析揭示了通气量和λ f之间明确联系的机制。结果进行了比较，一个对齐的建筑阵列的等效峡谷纵横比A R eff。这些偏离反映了理想化城市地形设置中未捕获的非线性效应。研究结果可为复杂地形下的城市通风参数化提供参考，并可为城市布局设计提供参考。
Ventilation has shown strong sensitivity to urban geometrical heterogeneity; however, the quantitative connection with the urban morphometric indices, eg the packing densities (λ f and λ p for the frontal and plan area, respectively) and the building-height variability (σ H), remains unclear. Using large-eddy simulation (LES), the dispersion of a pollutant scalar is investigated for turbulent boundary-layer (TBL) flows developed over real urban regions. While the time history of the domain averaged concentrations follow the familiar exponentially decaying function for all cases, the decay rates differ and there is a clear monotonic dependence on λ f. The mean tracer age, τ a, exhibits a strong linear scaling with λ f as well (R 2= 0. 8); however, an unambiguous relationship is hard to be discerned for the ventilation timescales versus the other morphometric indices (eg λ p and σ H). An effective canyon aspect ratio (A R eff) is proposed for real urban districts, which allows ventilation to be quantified in a simpler manner as that for idealised canyons. The age spectrum, which measures the probability density function of tracer ages across multiple timescales, is analysed to reveal the mechanisms underlying the well-defined connection between ventilation and λ f. Results are compared with that for an aligned building array of an equivalent canyon aspect ratio to A R eff. The departures reflect the nonlinear effects that are not captured in idealised urban topography setups. The results could be useful for the parameterisation of ventilation in urban areas of complex geometrical profiles and may serve as a reference for urban layout design towards optimum active ventilation capability.