Title: Instabilities and bifurcations in turbulent porous media flow Show Chinese title

Title: 湍流多孔介质流中的不稳定性与分岔

Abstract: Microscale turbulent flow in porous media is conducive to the development of flow instabilities due to strong vortical and shearing flow occurring within the pore space. When the flow instabilities around individual solid obstacles interact with numerous others within the porous medium, unique symmetry-breaking phenomena emerge as a result. This paper focuses on investigations of the vortex dynamics and flow instabilities behind solid obstacles in porous media, emphasizing how solid obstacle geometry and porosity influence both microscale and macroscale flow behavior. Two distinct symmetry-breaking mechanisms were identified in different porosity ranges. In low porosity media (< 0.8), a "deviatory flow" phenomenon occurs, where the macroscale flow deviates from the direction of applied pressure gradient at Reynolds numbers above 500. Deviatory flow is a source of macroscale Reynolds stress anisotropy, which is counterbalanced by a diminished vortex core size. In the intermediate porosity regime (0.8-0.95), a "jetting flow" mechanism creates asymmetric microscale velocity channels in the pore space through temporally biased vortex shedding, occurring during the transition to turbulence. Both symmetry-breaking phenomena are critically influenced by solid obstacle shape, porosity, and Reynolds number. Circularity of solid obstacle geometry and an adequately high Reynolds number provide critical conditions for symmetry-breaking, whereas porosity can be used to parametrize the degree of symmetry-breaking. This paper provides fundamental insights into the intricate flow dynamics in porous media, offering a comprehensive understanding of how microscale vortex interactions generate macroscale flow asymmetries across different geometric configurations. Show Chinese abstract

Abstract: 微尺度湍流在多孔介质中由于孔隙空间内强烈的涡旋和剪切流动，有助于流动不稳定的形成。 当单个固体障碍物周围的流动不稳定性与其他众多障碍物相互作用时，会因对称性破缺现象而出现独特的情况。 本文专注于研究多孔介质中固体障碍物后的涡旋动力学和流动不稳定性，强调固体障碍物的几何形状和孔隙率如何影响微观和宏观流动行为。 在不同的孔隙率范围内识别出两种不同的对称性破缺机制。 在低孔隙率介质（< 0.8）中，会发生“偏转流动”现象，即在雷诺数高于500时，宏观流动方向偏离施加的压力梯度。 偏转流动是宏观雷诺应力各向异性的来源，这种各向异性由减小的涡核尺寸来平衡。 在中间孔隙率范围（0.8-0.95）中，“射流流动”机制通过时间偏向的涡旋脱落，在孔隙空间中产生不对称的微观速度通道，发生在过渡到湍流期间。 这两种对称性破缺现象都受到固体障碍物形状、孔隙率和雷诺数的显著影响。 固体障碍物几何形状的圆度和足够高的雷诺数为对称性破缺提供了关键条件，而孔隙率可以用来参数化对称性破缺的程度。 本文提供了对多孔介质中复杂流动动力学的基本见解，全面理解了微观涡旋相互作用如何在不同几何配置下产生宏观流动不对称性。