Abstract This paper presents a study on the turbulent structure of the wind velocity field around a rectangular prism building model, calculated using large-eddy simulation. Spectral proper orthogonal decomposition (SPOD), a technique to perform proper orthogonal decomposition (POD) in the frequency domain, was applied to extract the physical phenomenon with the largest kinetic energy from the velocity field on a plane near the ground. The obtained fluctuation modes were periodic functions, sorted by frequencies, and provided an insight into the spatiotemporal structures of various physical phenomena within the turbulence field, including the Karman-type and arch-type vortex shedding and the flow separation phenomenon. The obtained eigenvalues depicted the kinetic energy distribution for all fluctuation modes, which was considered useful for understanding pedestrian-level wind. The results were compared for two cases (with and without fluctuation at the inflow boundary), which depicted the effect of the inflow fluctuation on the turbulent structures around the building. Additionally, for each physical phenomenon, the two modes calculated by POD were found quite similar to the real and imaginary parts of the SPOD eigenfunction. This indicates that POD needed two modes to depict each of the simple harmonic motions which were successfully detected by SPOD.

中文翻译：

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使用谱适当正交分解分析矩形棱柱建筑模型周围的湍流结构

摘要 本文研究了使用大涡模拟计算的矩形棱柱建筑模型周围风速场的湍流结构。频谱适当正交分解（SPOD）是一种在频域中执行适当正交分解（POD）的技术，用于从接近地面的平面上的速度场中提取具有最大动能的物理现象。得到的涨落模式是周期函数，按频率排序，可以洞察湍流场内各种物理现象的时空结构，包括卡门型和拱型涡旋脱落以及流动分离现象。获得的特征值描述了所有波动模式的动能分布，这被认为有助于理解行人级别的风。对两种情况（在流入边界有波动和没有波动）的结果进行了比较，这描述了流入波动对建筑物周围湍流结构的影响。此外，对于每种物理现象，发现 POD 计算的两种模式与 SPOD 特征函数的实部和虚部非常相似。这表明 POD 需要两种模式来描述 SPOD 成功检测到的每个简谐运动。发现 POD 计算的两种模式与 SPOD 特征函数的实部和虚部非常相似。这表明 POD 需要两种模式来描述 SPOD 成功检测到的每个简谐运动。发现 POD 计算的两种模式与 SPOD 特征函数的实部和虚部非常相似。这表明 POD 需要两种模式来描述 SPOD 成功检测到的每个简谐运动。