论文标题
剪切厚的液体径向位移期间瞬态反向手指的出现
Emergence of transient reverse fingers during radial displacement of a shear-thickening fluid
论文作者
论文摘要
高度剪切的颗粒玉米淀粉颗粒的致密水性悬浮液显示丰富的非线性流变学。我们以前曾证明，当剪切粉碎的玉米淀粉悬架被牛顿流体移位时，界面不稳定性的生长和发作，并提出了提高位移效率最大化的方法[Palak，R。Sathayanath，S。K. K. Kalpathy和R. Bandyopadhyay，Colloids Surf。物理化学。工程。 ASP。，629（2021）127405]。在目前的工作中，我们探讨了在准二维径向辐射hele-shaw细胞中，其不连续的缩短塑性方案中致密的玉米淀粉悬浮液的流离失所。我们系统地研究水与玉米淀粉之间的内部界面的生长动力学，以及悬浮液和空气之间的外界面的生长动力学。除了内部界面处的界面不稳定性的生长外，我们还观察到悬架的短暂戒断和外部界面处的指法不稳定性的形成。我们证明，这些“反向指法”不稳定性对水的注入流量，Hele-shaw细胞的间隙以及移位的玉米淀粉悬架的浓度极为敏感，而不管流体对之间的不混溶性如何。我们认为，随着玉米淀粉悬浮液由于位移流体施加的高剪切速率而扩张时，外部悬架空气界面会以恢复力响应，从而导致空气渗透到悬架中并形成反向手指。我们注意到，反向手指的生长大大降低了悬架的位移效率。最后，我们通过计算强度在密度密度悬浮液中传播的速度来证明内部和外界面模式的生长相关。我们的发现有助于通过受约束的几何形状理解颗粒材料的流动，并且可以扩展以研究剪切厚的材料中的应力传播，因为突然施加了高剪切速率，例如撞击行为。
A highly sheared dense aqueous suspension of granular cornstarch particles displays rich nonlinear rheology. We had previously demonstrated the growth and onset of interfacial instabilities when shear-thinning cornstarch suspensions were displaced by a Newtonian fluid, and had suggested methods to maximise displacement efficiency [Palak, R. Sathayanath, S. K. Kalpathy and R. Bandyopadhyay, Colloids Surf. A Physicochem. Eng. Asp., 629 (2021) 127405]. In the present work, we explore the miscible displacement of a dense aqueous cornstarch suspension in its discontinuous shear-thickening regime in a quasi-two-dimensional radial Hele-Shaw cell. We systematically study the growth kinetics of the inner interface between water and the cornstarch suspension, and also of the outer interface between the suspension and air. In addition to the growth of interfacial instabilities at the inner interface, we observe a transient withdrawal of the suspension and the formation of fingering instabilities at the outer interface. We demonstrate that these `reverse fingering' instabilities are extremely sensitive to the injection flow rate of water, the gap of the Hele-Shaw cell and the concentration of the displaced cornstarch suspension, {and emerge irrespective of immiscibility between the fluid pair. We believe that as the cornstarch suspension dilates due to the high shear rate imposed by the displacing fluid, the outer suspension-air interface responds with a restoring force, resulting in the penetration of air into the suspension and the formation of reverse fingers. We note that the growth of reverse fingers significantly reduces the displacement efficiency of the suspension. Finally, we demonstrate a correlation in the growth of inner and outer interfacial patterns by computing the velocity with which stresses propagate in the confined dense suspension. Our findings are useful in understanding the flow of granular materials through constrained geometries and can be extended to study stress propagation in shear-thickening materials due to a sudden imposition of high shear rate, such as in impact behaviour.
