Asymmetric flows of complex fluids past confined cylinders: A comprehensive numerical study with experimental validation
Asymmetric flows of complex fluids past confined cylinders: A comprehensive numerical study with experimental validation
复制标题
DOI：
10.1063/5.0008783
复制
发表时间：
2020-05
影响因子：
4.6
通讯作者：
S. Varchanis;Cameron C. Hopkins;A. Shen;J. Tsamopoulos;S. Haward
中科院分区：
文献类型：
--
作者：
S. Varchanis;Cameron C. Hopkins;A. Shen;J. Tsamopoulos;S. Haward
采用三个非牛顿本构模型来研究流体流变特性如何影响横向非对称流动通过受限圆柱体的发展。首先，将剪切减薄非弹性carau - yasuda模型的模拟与半稀黄原胶溶液的互补流速测量实验进行了比较，结果表明剪切减薄本身不足以引起流动不对称。其次，将弹性但非剪切减薄有限可扩展非线性弹性哑铃模型的模拟与聚环氧乙烷（PEO）在甘油水溶液中恒粘度溶液的实验进行了比较。模拟和实验表明，由于在驻点处产生的弹性应力，下游尾迹的扩展发展，但没有显示出围绕圆柱体两侧的流动的显著横向不对称性。最后，将弹性和剪切减薄线性Phan-Thien-Tanner （l-PTT）模型与实验测速法在流变相似的水中PEO溶液中进行了比较。在这里，在低流速下，横向对称被保留，而下游弹性尾迹的增长被观察到，在定性上类似于非剪切变薄的弹性流体。然而，在临界流量以上，流动分岔为稳定和稳定两种侧向不对称状态之一。进一步的参数研究与l-PTT模型进行了不同程度的剪切减薄和弹性，并修改了约束柱。这些试验证实了剪切减薄和弹性之间的耦合对不对称流动的发生的重要性，并建立了描述稳定和不稳定流动状态的稳定性和分岔图。
Three non-Newtonian constitutive models are employed to investigate how fluid rheological properties influence the development of laterally asymmetric flows past confined cylinders. First, simulations with the shear-thinning but inelastic Carreau–Yasuda model are compared against complementary flow velocimetry experiments on a semidilute xanthan gum solution, showing that shear-thinning alone is insufficient to cause flow asymmetry. Next, simulations with an elastic but non-shear-thinning finitely extensible non-linear elastic dumbbell model are compared with experiments on a constant viscosity solution of poly(ethylene oxide) (PEO) in an aqueous glycerol mixture. The simulations and the experiments reveal the development of an extended downstream wake due to elastic stresses generated at the stagnation point but show no significant lateral asymmetries of the flow around the sides of the cylinder. Finally, the elastic and shear-thinning linear Phan–Thien–Tanner (l-PTT) model is compared with experimental velocimetry on a rheologically similar solution of PEO in water. Here, at low flow rates, lateral symmetry is retained, while the growth of a downstream elastic wake is observed, in qualitative similarity to the non-shear-thinning elastic fluids. However, above a critical flow rate, the flow bifurcates to one of the two stable and steady laterally asymmetric states. Further parameter studies with the l-PTT model are performed by varying the degrees of shear-thinning and elasticity and also modifying the confinement of the cylinder. These tests confirm the importance of the coupling between shear-thinning and elasticity for the onset of asymmetric flows and also establish stability and bifurcation diagrams delineating the stable and unstable flow states.