Effects of elasticity and flow ramp up on kinetics of shear banding flow formation in wormlike micellar fluids
Effects of elasticity and flow ramp up on kinetics of shear banding flow formation in wormlike micellar fluids
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DOI：
10.1122/8.0000010
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发表时间：
2020-08
影响因子：
3.3
通讯作者：
Peter Rassolov;Hadi Mohammadigoushki
中科院分区：
文献类型：
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作者：
Peter Rassolov;Hadi Mohammadigoushki
我们报告了泰勒-库埃特（TC）细胞中流动开始时剪切带蠕虫状胶束中速度分布的时空演化的实验。中度纠缠和高度纠缠解决方案均在广泛的流体弹性 E 范围内进行考虑。流体弹性 E = Wi/Re，表征弹性对惯性效应的相对重要性。对于中度和高度缠结的解决方案，在剪切开始时，以及在应力衰减期间，流体在间隙子集中以与施加运动相反的方向移动，超过弹性和流量上升速率的临界阈值，这取决于流体缠结密度。令人惊讶的是，超过流体弹性的第二个临界阈值，瞬态回流在适度缠结的溶液中消失，突出了胶束缠结对剪切带系统中流动瞬态演化的重要性。更有趣的是，我们报告了在一定的流体弹性和流量斜坡上升率条件下形成多带准稳态速度剖面。多带剖面的特征是内圆柱附近有一个低剪切带，TC间隙中间有一个高剪切带，外圆柱附近有另一个低剪切带。最后，我们表明，对于高度纠缠的溶液，TC 单元内筒处的表观壁滑移更为明显，并且随着流体弹性的增加而减小。将实验观察结果与 Vasquez-Cook-McKinley 模型的现有模拟进行比较，并对未来的模拟提出了一些建议。
We report experiments on spatiotemporal evolution of the velocity profiles in shear-banding wormlike micelles upon inception of the flow in a Taylor–Couette (TC) cell. Both moderately entangled and highly entangled solutions are considered over a broad range of fluid elasticity E. Fluid elasticity, E = Wi/Re, characterizes the relative importance of the elastic to inertial effects. For both moderately and highly entangled solutions, upon inception of the shear, and during the stress decay period, fluid moves in the opposite direction to that of the imposed motion in a subset of the gap beyond critical thresholds of elasticity and flow ramp up rate, which depend on the fluid entanglement density. Surprisingly, beyond a second critical threshold of the fluid elasticity, the transient backflow disappears in moderately entangled solutions, highlighting the importance of the micellar entanglement on transient evolution of the flow in shear banding systems. More interestingly, we report the formation of multibanded quasisteady velocity profiles under certain conditions of fluid elasticity and flow ramp up rate. The multibanded profiles are characterized by a low shear band near the inner cylinder, a high shear band in the middle of the TC gap, and another low shear band near the outer cylinder. Finally, we show that the apparent wall slip at the inner cylinder of the TC cell is more pronounced for highly entangled solutions and decreases as the fluid elasticity increases. Experimental observations are compared with the existing simulations of the Vasquez–Cook–McKinley model, and several suggestions are made for future simulations.