简化城市流场中拱形涡的数据驱动评估
Data-driven assessment of arch vortices in simplified urban flows
AI总结：
本文利用HODMD、POD和STKD等数据驱动方法分析简化城市流场，识别并分类与拱形涡相关的低频涡生成模态和高频涡破碎模态，揭示二者相互作用是驱动建筑物间涡结构形成与破坏及流动动力学的关键机制。
摘要：
理解城市区域中的流动结构被广泛认为是一项具有挑战性的问题，因为它对城市发展、空气质量和污染物扩散具有重要影响。在本研究中，采用最先进的数据驱动方法对简化城市流场进行模态分析，以研究这些环境中的主导流动过程。高阶动态模态分解（HODMD）是一种分析湍流的高效方法，它与本征正交分解（POD）等传统技术一起被用于分析简化城市环境的高保真模拟数据。此外，时空库普曼分解（STKD）将被应用于HODMD获得的时间模态，以进行空间分析。冠层内的流动相互作用影响流动结构，尤其是拱形涡。后者是一种通常出现在壁面障碍物下游的涡结构，由流动分离产生。因此，本研究的主要目标是刻画在不同几何形状的城市区域中促进这些现象形成的机制。值得注意的是，在HODMD算法识别的所有涡结构中，低频和高频模态根据它们与拱形涡的关系被分类。它们分别被称为涡生成模态和涡破碎模态。这种分类意味着，驱动建筑物之间主要涡结构形成和破坏的过程之一是低频和高频结构之间的相互作用。POD揭示的涡破碎模态的高能量表明，这一破坏过程是驱动流动动力学的机制。
英文摘要：
Understanding flow structures in urban areas is widely recognized as a challenging concern due to its effect on urban development, air quality, and pollutant dispersion. In this study, state-of-the-art data-driven methods for modal analysis of simplified urban flows are used to study the dominant flow processes in these environments. Higher order dynamic mode decomposition (HODMD), a highly-efficient method to analyze turbulent flows, is used together with traditional techniques such as proper-orthogonal decomposition (POD) to analyze high-fidelity simulation data of a simplified urban environment. Furthermore, the spatio-temporal Koopman decomposition (STKD) will be applied to the temporal modes obtained with HODMD to perform spatial analysis. The flow interaction within the canopy influences the flow structures, particularly the arch vortex. The latter is a vortical structure generally found downstream of wall-mounted obstacles, which is generated as a consequence of flow separation. Therefore, the main objective of the present study is to characterize the mechanisms that promote these phenomena in urban areas with different geometries. Remarkably, among all the vortical structures identified by the HODMD algorithm, low- and high-frequency modes are classified according to their relation with the arch vortex. They are referred to as vortex-generator and vortex-breaker modes, respectively. This classification implies that one of the processes driving the formation and destruction of major vortical structures in between the buildings is the interaction between low- and high-frequency structures. The high energy revealed by the POD for the vortex-breaker modes points to this destruction process as the mechanism driving the flow dynamics.
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