Abstract The understanding of nonlinear flow in rough-walled rock fractures is critical for underground engineering and geological sciences. The macroscopic behavior and microfluidic field of flow in rough-walled artificial fracture models was investigated through microscopic visualization of hydraulic experiment. The results indicate that there are three states of flow regime in fracture, namely linear, weak inertial and strong inertial. In linear flow regime, the relationship between pressure drops and flow rate is linear, and all the streamlines in the microfluidic field are parallel. In weak inertial flow regime, pressure drop and flow become nonlinear, and the inertial pressure loss is less than the viscous pressure loss. Moreover, backflow occurs near the tortuous wall in the microfluidic field. In strong inertial flow regime, the inertial pressure loss is greater than viscous pressure loss, and the backflow begins to detach from the wall and eventually develop into a significantly large eddy far away from the wall. However, the flow in the mainstream remains laminar rather than turbulent in this experiment. This result indicates that the main cause of the nonlinearity of flow in fracture is eddies due to the increase of the inertia term and the variation of aperture. The shrinking of effective channel and losing of kinetic energy caused by eddies make fluid flow nonlinear. Moreover, the area and number of eddies depend on the fracture roughness and the Reynolds number.

中文翻译：

---

粗糙壁人工裂缝模型中非线性流动宏观行为和微流体场的实验研究

摘要 理解粗糙壁岩石裂缝中的非线性流动对于地下工程和地质科学至关重要。通过水力实验的微观可视化研究了粗糙壁人工裂缝模型中流动的宏观行为和微流体场。结果表明，裂缝中存在三种流态，即线性、弱惯性和强惯性。在线性流态中，压降与流速之间的关系是线性的，微流体场中的所有流线都是平行的。在弱惯性流态下，压降和流量呈非线性，惯性压力损失小于粘性压力损失。此外，回流发生在微流体场中曲折壁附近。在强惯性流态下，惯性压力损失大于粘性压力损失，回流开始脱离壁面，最终发展成远离壁面的明显大涡。然而，在这个实验中，主流中的流动仍然是层流而不是湍流。该结果表明，裂缝中流动非线性的主要原因是惯性项增加和孔径变化引起的涡流。涡流引起的有效通道收缩和动能损失使流体流动呈非线性。此外，涡流的面积和数量取决于断裂粗糙度和雷诺数。在这个实验中，主流中的流动保持层流而不是湍流。该结果表明，裂缝中流动非线性的主要原因是惯性项增加和孔径变化引起的涡流。涡流引起的有效通道收缩和动能损失使流体流动呈非线性。此外，涡流的面积和数量取决于断裂粗糙度和雷诺数。在这个实验中，主流中的流动保持层流而不是湍流。该结果表明，裂缝中流动非线性的主要原因是惯性项增加和孔径变化引起的涡流。涡流引起的有效通道收缩和动能损失使流体流动呈非线性。此外，涡流的面积和数量取决于断裂粗糙度和雷诺数。