We present results from water-channel experiments on neutrally-stable turbulent flows over staggered arrays of cubical obstacles modelling idealised urban canopies. Attention is concentrated on the vertical profiles of the Eulerian (T^E) and Lagrangian (T^L) time scales of the turbulence above three canopies with different plan area fractions (λ_P = 0.1, 0.25 and 0.4). The results show that both the streamwise and vertical components of T^L increase approximately linearly with height above the obstacles, supporting Raupach’s linear law. The comparisons with the Lagrangian time scales over canyon-type canopies in the skimming flow and wake interference regimes show that the staggered configuration of cubical obstacles increases the streamwise T^L, while decreasing its vertical counterpart. A good agreement has also been found between the eddy viscosities (K_T) estimated by applying Taylor’s theory and the classical first order closure relating the momentum flux to the velocity gradient. The results show that K_T obeys Prandtl’s theory, particularly for λ_P = 0.25 and 0.4.

中文翻译：

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错列立方障碍物上方湍流的欧拉和拉格朗日时间尺度

我们目前在模拟理想化城市雨棚的立方障碍物交错阵列上进行中性稳定湍流水通道实验的结果。注意力集中在欧拉（垂直剖面Ť ^ë）和拉格朗日（Ť^大号以上三个檐用不同的计划面积分数的紊流的）时间尺度（λ _P  = 0.1，0.25和0.4）。结果表明，两者的流向和垂直分量Ť^大号高度随着障碍物上方的高度而线性增加，从而支持Raupach的线性定律。在掠流和尾流干扰状态下，对峡谷型冠层的拉格朗日时间尺度的比较表明，立方障碍物的交错配置增加了水流T ^L，同时减小了其垂直对应物。在通过应用泰勒理论估计的涡流粘度（K _T）和将动量通量与速度梯度相关的经典一阶闭合之间也发现了很好的一致性。结果表明，ķ _Ť服从普朗特的理论，尤其是对于λ _P  = 0.25和0.4。