Control of Pressure Gradient-Driven Spatio-temporal Patterns in Strongly Correlated Soft Materials

Saffinan-Taylor不稳定性（即指进模式从Saffinan-Taylor向尖端分裂模式的变化）首次出现时的起始剪切速率2V_f/B与被驱替的强相关软材料（如聚合物溶液、悬浮液和乳液）的流变性质显示非牛顿行为（与材料无关）时的起始剪切速率2V_f/B符合得很好。指生长的平均速度几乎与修正的达西定律一致，其中粘度被剪切速率依赖性粘度取代，而与注入流体和Hele-Shaw单元无关。由于吸附在空气-水界面上的HPMC层的粘弹性，气泡的运动由单调振动变为阻尼直线运动。在Strouhal数为0.2以下，在上升气泡后面的尾流中观察到卡门涡街，而在Strouhal数为0.2以上，尾流结构不同于卡门涡街。这种差异应归因于从卡门流动到湍流流动的变化。

The onset imposed shear rate 2V_f/b at which the Saffinan-Taylor instability, namely changes in the fingering pattern from the Saffinan-Taylor to the tip splitting ones occur for the first time, is in good agreement with that where the rheological properties of the displaced strongly correlated soft materials, such as polymer solutions, suspensions, and emulsions show non-Newtonian behavior irrespective of the material. The average velocity of the finger growth is almost coincident with that of the modified Darcy's law, in which the viscosity is displaced by the shear rate dependent viscosity, irrespective of the injected fluid and the Hele-Shaw cell. Therefore, the fundamental equation of viscous fingering in the soft materials can be obtained for the finger growth and it seems to be useful further to develop theoretical works and computer simulations for their viscous fingering results.The bubble motion is changed from monotonous vibration to straight paths through damped one, due to the viscoelastic properties of the HPMC layer adsorbed at the air-water interface. Below the Strouhal number of 0.2, the Karman vortex street is observed in the wake behind rising bubbles, whereas above the Strouhal number of 0.2, the wake structures are different from the Karman vortex street. The difference should be attributed to changes in flow from the Karman to turbulent flow.