The characteristics of large- and small-scale turbulent motions at roof-level in a street canyon flow were experimentally investigated along with their spatio-temporal organization and their mutual interaction in this region. Quadrant analysis was conducted to identify sweep and ejection events, whilst a spanwise spatial filter was used to identify the large-scale motions in the flow. The present analysis was conducted for six configurations; three upstream roughness arrays and two canyon width (W) to height (h) aspect ratios (AR = W/h = 1 and 3). The upstream roughness arrays consisted of three-dimensional cubes (plan area density, λ_p = 25%), 1h spaced two-dimensional bars (λ_p = 50%, corresponding to the skimming-flow regime) and 3h spaced two-dimensional bars (λ_p = 25%, corresponding to the wake-interference flow regime). It was found that the roughness configuration has a strong effect on the size of the quadrant events in the street canyon, with the wake-interference flow regimes producing significantly larger sweep and ejection events than the skimming-flow regimes. Upstream wake-interference flow regimes were found to have a significantly greater temporal correlation than in the skimming-flow regimes. Large-scale streamwise and spanwise velocity components were found to have large spatio-temporal correlation integral scales, in agreement with the large-scale structures existing in the overlying boundary layer. It was also confirmed that there is a coupling between large- and small-scales at roof-level of the street canyon. While sweep and ejection events were found to be due to the dynamical contribution of the small-scales, their occurrence is shown to be coupled with that of large-scale low- and high-momentum regions, respectively.

中文翻译：

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街道峡谷流中的屋顶大大小小相干结构

通过实验研究了街道峡谷流中屋顶水平的大尺度和小尺度湍流运动的特征，以及它们在该地区的时空组织及其相互影响。进行象限分析以识别扫掠和喷射事件，同时使用翼展方向空间滤波器识别流中的大规模运动。本分析针对六种配置进行；三个上游粗糙度阵列和两个峡谷宽度（W）与高度（h）的宽高比（AR =  W / h  = 1和3）。上游粗糙度阵列组成的三维立方体（平面面积密度，λ _p  = 25％），1个H ^间隔二维杆（λ_p  = 50％，对应于该侧录-流态）和3 ħ间隔二维杆（ λ _p = 25％，对应于尾波干扰流态）。已发现，粗糙度构造对街道峡谷中象限事件的大小有很大影响，尾流干扰流态比扫掠流态产生的扫掠和喷射事件要大得多。已发现上游尾流干扰流态的时间相关性比撇油流态大。发现大规模的沿河流速度和跨度的速度分量具有较大的时空相关积分尺度，这与上覆边界层中存在的大规模结构一致。还证实了在街道峡谷的屋顶高度上的大尺度和小尺度之间存在耦合。