This study expands the study conducted by Zhang et al. (Boundary-Layer Meteorol, 2022, Vol. 183, 97–123) to elucidate turbulent structures within an ideal two-dimensional street canyon, and determine their contribution to pollutant removal. In response to the limitations of the reference study wherein spanwise turbulent structures were not elucidated, an advanced technique called spectral proper orthogonal decomposition (SPOD) with two-dimensional Fourier transformation was applied in the current study. This approach combined proper orthogonal decomposition along the spatial streamwise and vertical directions and Fourier decomposition along the time and spatial spanwise direction. Using this technique, various fluctuation patterns were reasonably decomposed and visualised according to their scales. In addition, their intensities and contributions to pollutant removal were quantitatively analysed using the SPOD spectrum and cospectra. The time scales of most energetic modes were found to be proportional to their spanwise length scales, regardless of their scales and flow mechanisms. The ranges of the spanwise wavenumber and frequency, at which pollutant removal events occurred at the roof level, were specified. These ranges coincided with those of small-scale structures caused by Kelvin–Helmholtz instabilities. Further complex analysis of the correlation between large- and small-scale structures showed that large-scale structures have a high possibility of indirectly enhancing or weakening pollutant removal by amplifying or suppressing small-scale structures. This occurred stochastically along both time and spanwise directions. Quantitatively, the amplitude of small-scale structures was amplified or suppressed by 13–16% on average by high- or low-momentum fluids.

这项研究扩展了张等人进行的研究。(Boundary-Layer Meteorol, 2022, Vol. 183, 97–123) 阐明理想二维街道峡谷内的湍流结构，并确定它们对污染物去除的贡献。为了响应参考研究的局限性，其中没有阐明展向湍流结构，在当前的研究中应用了一种称为光谱适当正交分解 (SPOD) 和二维傅里叶变换的先进技术。该方法结合了沿空间流向和垂直方向的适当正交分解和沿时间和空间跨度方向的傅里叶分解。使用这种技术，各种波动模式根据它们的尺度被合理地分解和可视化。此外，使用 SPOD 光谱和余光谱定量分析了它们的强度和对污染物去除的贡献。大多数高能模式的时间尺度被发现与它们的跨度长度尺度成正比，而不管它们的尺度和流动机制如何。指定了在屋顶水平发生污染物去除事件的跨度波数和频率的范围。这些范围与开尔文-亥姆霍兹不稳定性引起的小尺度结构相吻合。对大型和小型结构之间相关性的进一步复杂分析表明，大型结构很可能通过放大或抑制小型结构来间接增强或削弱污染物去除。这沿着时间和跨度方向随机发生。数量上，