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.

中文翻译：

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弹性和流量增加对蠕虫状胶束流体中剪切带流形成动力学的影响

我们报告了在 Taylor-Couette (TC) 细胞中流动开始时剪切带状蠕虫状胶束中速度分布的时空演化实验。中度纠缠和高度纠缠的解决方案都被考虑在广泛的流体弹性 E 范围内。流体弹性，E = Wi/Re，表征弹性对惯性效应的相对重要性。对于中度和高度纠缠的解决方案，在剪切开始时以及在应力衰减期间，流体以与超出弹性和流动斜率临界阈值的间隙子集中的强加运动相反的方向移动，这取决于流体纠缠密度。令人惊讶的是，超过流体弹性的第二个临界阈值，瞬时回流在适度纠缠的溶液中消失，强调胶束纠缠对剪切带系统中流动的瞬态演变的重要性。更有趣的是，我们报告了在流体弹性和流量上升速率的某些条件下多带准稳态速度剖面的形成。多带剖面的特点是内圆柱附近有一个低剪切带，TC间隙中部有一个高剪切带，外圆柱附近还有一个低剪切带。最后，我们表明，对于高度缠结的溶液，TC 单元内圆柱体的表观壁滑移更明显，并且随着流体弹性的增加而减小。实验观察结果与 Vasquez-Cook-McKinley 模型的现有模拟进行了比较，并对未来的模拟提出了一些建议。