Taylor-Couette flow of polymer solutions with shear-thinning and viscoelastic rheology
Taylor-Couette flow of polymer solutions with shear-thinning and viscoelastic rheology
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DOI：
10.1017/jfm.2020.701
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发表时间：
2020-12-25
影响因子：
3.7
通讯作者：
Balabani, Stavroula
中科院分区：
文献类型：
--
作者：
Cagney, Neil;Lacassagne, Tom;Balabani, Stavroula
我们研究泰勒-库埃特流动的甘油-水混合物含有一个广泛的浓度范围（0-2000 ppm）的黄原胶，这诱导剪切稀化和粘弹性，以评估各种流动不稳定性的流变学的变化的影响。对于每种悬浮液，雷诺数（惯性力与粘性力之比）缓慢增加到约1000的峰值，并使用流动可视化连续监测流动。剪切变稀被发现抑制许多弹性控制的不稳定性，已经观察到在以前的研究中的粘弹性泰勒-库埃特流，如扰动和无序振荡。聚合物的加入降低了形成泰勒涡的临界雷诺数，但延迟了波动流的发生。然而，在粘弹性制度（浓度），泰勒涡的形成后不久，流动变得高度不稳定，与雷诺数，这是高度可重复的波度的实质性变化。旋涡被发现突然合并的雷诺数的增加，随着聚合物浓度的增加，合并的数量。波长的这些突变是高度滞后的，并且可以在稳定和波动状态中发生。最后，在中等和密集的聚合物溶液中的旋涡被证明是经历了一个逐渐漂移的大小和位置，这似乎是密切相关的分裂和合并的旋涡。
We study Taylor-Couette flow of a glycerol-water mixture containing a wide range of concentration (0-2000 ppm) of xanthan gum, which induces both shear-thinning and viscoelasticity, in order to assess the effect of the changes in rheology on various flow instabilities. For each suspension, the Reynolds number (the ratio of inertial to viscous forces) is slowly increased to a peak value of around 1000, and the flow is monitored continuously using flow visualisation. Shear-thinning is found to suppress many elasticity-controlled instabilities that have been observed in previous studies of viscoelastic Taylor-Couette flow, such as diwhirls and disordered oscillations. The addition of polymers is found to reduce the critical Reynolds number for the formation of Taylor vortices, but delay the onset of wavy flow. However, in the viscoelastic regime (concentration), the flow becomes highly unsteady soon after the formation of Taylor vortices, with substantial changes in the waviness with Reynolds number, which are shown to be highly repeatable. Vortices are found to suddenly merge as the Reynolds number increases, with the number of mergers increasing with polymer concentration. These abrupt changes in wavelength are highly hysteretic and can occur in both steady and wavy regimes. Finally, the vortices in moderate and dense polymer solutions are shown to undergo a gradual drift in both their size and position, which appears to be closely linked to the splitting and merger of vortices.