This paper investigates the dynamics governing turbulent momentum exchange and heat transfer between pore flow within porous media and the turbulent flow passing over it. Employing high-fidelity pore-scale large eddy simulation, our investigation explores the fundamental mechanisms driving these phenomena. Modal analysis based on snapshot proper orthogonal decomposition (POD) is employed to quantify the modes of interaction between porous and non-porous regions, providing a comprehensive understanding of the underlying processes. Spatial and temporal modes reveal the existence of localized flow structures at the pore scale, contributing to time-varying patterns of information exchange. At the commencement of the porous block, the mean flow (Mode = 0) from the porous to non-porous region is the dominant mechanism in momentum exchange and heat transfer. This mode facilitates convective heat transfer from the porous to the non-porous region through upward and forward flow movements, showcasing positive flow leakage. In addition to the mean flow, the turbulent flux inherent in alternate POD modes (Mode ≠ 0) plays a substantial role in information propagation, influencing diverse directions. Spatial modes, complemented by statistical analysis, uncover a significant likelihood of observing negative vertical velocity values in the wake of the porous ligaments at the porous-fluid interface, indicative of negative flow leakage. This negative flow leakage precisely corresponds to the local penetration of fluid from the non-porous region into the porous region. Furthermore, our study reveals that information exchange via turbulence fluctuations manifests through complex outward and inward interactions in regions characterized by substantial positive flow leakage. Notably, these regions exhibit a distinct tendency for high-momentum streamwise-oriented flow to migrate outward from the porous region into the non-porous region (outward interactions). Conversely, inward interactions arise in these regions when the instantaneous magnitude of positive flow leakage is smaller than the mean value of positive flow leakage, emphasizing the pulsating nature of positive flow leakage. Finally, the distribution of the Nusselt number highlights that more than 60% of total heat transfer occurs within the initial one-third of the porous block length. Significantly, a notable portion of the porous ligaments experiences insufficient cooling due to positive flow leakage, underlining the critical implications of these findings for the understanding of turbulent momentum exchange and heat transfer in a composite porous-fluid system.

中文翻译：

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复合多孔流体系统中湍流动量交换和传热的数据驱动模态分析

本文研究了控制多孔介质内的孔隙流与流经其上的湍流之间的湍流动量交换和传热的动力学。我们的研究采用高保真度孔隙尺度大涡模拟，探索了驱动这些现象的基本机制。采用基于快照本征正交分解 (POD) 的模态分析来量化多孔区域和非多孔区域之间的相互作用模式，从而提供对底层过程的全面理解。空间和时间模式揭示了孔隙尺度局部流动结构的存在，有助于信息交换的时变模式。在多孔块开始时，从多孔区域到无孔区域的平均流量（众数 = 0）是动量交换和传热的主要机制。这种模式通过向上和向前的流动运动促进从多孔区域到无孔区域的对流热传递，表现出正向流动泄漏。除了平均流之外，交替 POD 模式（Mode ≠ 0）中固有的湍流在信息传播中发挥着重要作用，影响不同的方向。空间模式，辅之以统计分析，揭示了在多孔流体界面处的多孔韧带之后观察到负垂直速度值的显着可能性，这表明负流量泄漏。该负流量泄漏精确地对应于流体从非多孔区域到多孔区域的局部渗透。此外，我们的研究表明，通过湍流波动进行的信息交换通过在以大量正流泄漏为特征的区域中复杂的向外和向内相互作用来体现。值得注意的是，这些区域表现出高动量流向流动从多孔区域向外迁移到无孔区域的明显趋势（向外相互作用）。相反，当正流泄漏的瞬时幅度小于正流泄漏的平均值时，在这些区域中出现向内相互作用，强调了正流泄漏的脉动性质。最后，努塞尔数的分布表明，超过 60% 的总传热发生在多孔块长度的初始三分之一内。值得注意的是，由于正向流动泄漏，多孔韧带的显着部分经历了不充分的冷却，强调了这些发现对于理解复合多孔流体系统中的湍流动量交换和传热的关键意义。