Turbulent flows over porous lattices consisting of rectangular cuboid pores are investigated using scale-resolving direct numerical simulations. Beyond a certain threshold which is primarily determined by the wall-normal Darcy permeability, ${{\mathsf{K}}_y}$ , near-wall turbulence transitions from its canonical regime, marked by the presence of streak-like structures, to another marked by the presence of Kelvin–Helmholtz-like (K–H-like) spanwise-coherent structures. The threshold agrees well with that previously established in studies where permeable-wall boundary conditions had been used as surrogates for a porous substrate (Gómez-de Segura & García-Mayoral, J. Fluid Mech., vol. 875, 2019, pp. 124–172). In the smooth-wall-like regime, none of the investigated substrates demonstrate any reduction in drag relative to a smooth-wall flow. At the permeable surface, a notable component of the flow is that which adheres to the pore geometry and undergoes modulation by the turbulent scales of motions due to the interaction mechanism described by Abderrahaman-Elena et al. (J. Fluid Mech., vol. 865, 2019, pp. 1042–1071). Its resulting effect can be quantified in terms of an amplitude modulation (AM) using the approach of Mathis et al. (J. Fluid Mech., vol. 628, 2009, pp. 311–337). This pore-coherent flow component persists throughout the porous substrate, highlighting the importance of a given substrate's microstructure in the presence of an overlying turbulent flow. This geometry-related aspect of the flow is not accounted for when continuum-based models for a porous medium or effective representations of them, such as wall boundary conditions, are used. The intensity of the AM effect is enhanced in the K–H-like regime and becomes strengthened with larger permeability. As a result, structured porous materials may be designed to exploit or mitigate these flow features depending upon the intended application.

中文翻译：

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多孔晶格上的湍流：近壁湍流的改变和孔隙流振幅调制

使用尺度解析直接数值模拟研究由矩形长方体孔组成的多孔晶格上的湍流。超过主要由壁正常达西渗透率决定的某个阈值， ${{\mathsf{K}}_y}$ ，近壁湍流从其典型状态（以存在条纹状结构为标志）过渡到另一个以存在开尔文-亥姆霍兹（K-H）样展向相干结构为标志的状态。该阈值与先前在研究中建立的阈值非常吻合，在这些研究中，渗透壁边界条件已被用作多孔基材的替代（Gómez-de Segura 和 García-Mayoral，J.流体机械。，卷。 875，2019 年，第 124-172 页）。在光滑壁状流态中，所研究的基材均未表现出相对于光滑壁流的阻力有任何减少。在可渗透表面，流动的一个显着成分是粘附在孔隙几何形状上的成分，并且由于 Abderrahaman-Elena 描述的相互作用机制而受到运动湍流尺度的调节。等人。（J.流体机械。，卷。 865，2019 年，第 1042–1071 页）。其产生的效果可以使用 Mathis 的方法根据幅度调制 (AM) 进行量化等人。（J.流体机械。，卷。 628，2009 年，第 311-337 页）。这种孔隙相干流成分持续存在于整个多孔基材中，突出了给定基材的微观结构在存在上覆湍流的情况下的重要性。当使用基于连续介质的多孔介质模型或它们的有效表示（例如壁边界条件）时，不会考虑流动的这种与几何相关的方面。 AM 效应的强度在类 K-H 区域中增强，并且随着渗透率的增大而增强。因此，结构化多孔材料可被设计为根据预期应用来利用或减轻这些流动特征。