Symmetry breaking of turbulent flow in porous media composed of periodically arranged solid obstacles
Symmetry breaking of turbulent flow in porous media composed of periodically arranged solid obstacles
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DOI：
10.1017/jfm.2021.813
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发表时间：
2018-10
影响因子：
3.7
通讯作者：
V. Srikanth;Ching-Wei Huang;T. Su;A. Kuznetsov
中科院分区：
文献类型：
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作者：
V. Srikanth;Ching-Wei Huang;T. Su;A. Kuznetsov
本文的重点是对周期性多孔介质中的流动动力学进行数值模拟研究，以分析对称性破坏现象的物理原因。对称性破坏现象是导致宏观流动方向偏离外加压力梯度方向的现象。对于圆形固体障碍物，孔隙率在0.43~0.72的范围内，这一现象最为突出。这是湍流区域中，固体障碍物上的表面力与流体流动的惯性力相互竞争而形成的流动不稳定性的结果。我们报道了周期性多孔介质中对称性破缺现象的起源和机制。用大涡模拟(LES)方法模拟了均匀多孔介质中的湍流流动，该介质由周期性的方形格子排列的柱状固体障碍物组成。用直接数值模拟方法模拟了对称性破裂过程中的暂态过程，并验证了大涡模拟方法的有效性。从以下几个方面进行了定量和定性的观测：(1)大尺度动量平衡；(2)二维和三维流动可视化。这种现象的根源在于涡旋脱落过程中出现的流动不稳定性的放大。对称破缺现象是一种干叉分叉现象，它可以根据局部涡脱脱过程呈现多种模式。观察到该现象对孔隙率、固体障碍物形状和雷诺数敏感。对于对称的固体障碍物几何形状，它是多孔介质中宏观湍流各向异性的来源。在宏观尺度上，雷诺应力张量的主轴不与任何几何对称轴对齐，也不与流动方向对齐。因此，多孔介质中的对称性破缺涉及未解决的流动物理问题，在宏观尺度上模拟流动的非均质性时应考虑这一点。
Abstract The focus of this paper is a numerical simulation study of the flow dynamics in a periodic porous medium to analyse the physics of a symmetry-breaking phenomenon, which causes a deviation in the direction of the macroscale flow from that of the applied pressure gradient. The phenomenon is prominent in the range of porosity from 0.43 to 0.72 for circular solid obstacles. It is the result of the flow instabilities formed when the surface forces on the solid obstacles compete with the inertial force of the fluid flow in the turbulent regime. We report the origin and mechanism of the symmetry-breaking phenomenon in periodic porous media. Large-eddy simulation (LES) is used to simulate turbulent flow in a homogeneous porous medium consisting of a periodic, square lattice arrangement of cylindrical solid obstacles. Direct numerical simulation is used to simulate the transient stages during symmetry breakdown and also to validate the LES method. Quantitative and qualitative observations are made from the following approaches: (1) macroscale momentum budget and (2) two- and three-dimensional flow visualization. The phenomenon draws its roots from the amplification of a flow instability that emerges from the vortex shedding process. The symmetry-breaking phenomenon is a pitchfork bifurcation that can exhibit multiple modes depending on the local vortex shedding process. The phenomenon is observed to be sensitive to the porosity, solid obstacle shape and Reynolds number. It is a source of macroscale turbulence anisotropy in porous media for symmetric solid-obstacle geometries. In the macroscale, the principal axis of the Reynolds stress tensor is not aligned with any of the geometric axes of symmetry, nor with the direction of flow. Thus, symmetry breaking in porous media involves unresolved flow physics that should be taken into consideration while modelling flow inhomogeneity in the macroscale.