出 处:《Acta Mechanica Sinica》2023年第6期198-211,共14页力学学报(英文版)
基 金:supported by the National Natural Science Foundation of China(Grant Nos.12222211 and 11972322).
摘 要:悬浮液的宏观流变特性往往与它们的微观结构变化密不可分,一些实验研究表明DLVO相互作用,即由于悬浮颗粒表面电荷而产生的微观排斥力和吸引力,对悬浮液的微观结构,特别是对团簇的形成有重大影响.在这项研究中,通过结合DLVO作用力与水动力和摩擦接触的数值模拟研究了非布朗悬浮液的流变特性及其微观结构.本文确定了不同的机制来解释排斥性和黏附性悬浮液的不同流变反应,揭示了颗粒团簇的演变和悬浮液流变学之间的重要联系.在排斥性系统中,排斥力和水动力之间的竞争以及由此产生的最小颗粒分离分布的变化是在低剪切率下第一次剪切变稀的原因.剪切增稠是在高剪切率下观察到的,并且由颗粒接触主导.吸引力的增强加大了悬浮液的黏度,同时掩盖了剪切增稠,即使在第一次剪切变稀的条件下,颗粒也会进行接触。第二法向应力差表现出与黏度相似的演变,而第一法向应力差主要是由波动主导的。微观结构分析显示,摩擦性团簇出现在排斥性悬浮液中,随着剪切率的增加,其数量和尺寸都在增长.另一方面,强吸引力悬浮液中的团簇会分解成更小的团簇,导致黏度降低.形状各向异性的计算表明,排斥性悬浮液中的摩擦性团簇倾向于在模拟箱中均匀地膨胀,而在高吸引强度下,团簇在强剪切时趋向于圆柱形.我们在微观结构方面的研究可以帮助弥合微观演化和宏观流变反应之间的差距,从而为非布朗悬浮液的本构模型的建立作出贡献.The macroscopic rheological properties of suspensions are often inextricably related to changes in their microstructure,and a number of experimental studies have demonstrated the significant influence of DLVO(Derjaguin-Landau-Verwey-Overbeek)in-teractions,namely microscopic repulsive and attractive forces due to surface charge on particles in suspensions,on the microstruc-ture of suspensions,especially on cluster formation.In this study,the rheological properties of non-Brownian suspensions and their microstructures are investigated by numerical simulations combining DLVO interactions with hydrodynamics and frictional contacts.Different mechanisms have been identified to account for diverse rheological responses of repulsive and adhesive sus-pensions,revealing a significant association between the evolution of particle clusters and suspension rheology.In repulsive systems,competitions between repulsive and hydrodynamic forces and the resulting change in the distribution of minimum par-ticle separation are responsible for the first shear thinning at low shear rates.Shear thickening is observed at high shear rates and is dominated by particles contacts.Enhancing attractive forces give rise to the viscosity of the suspensions while obscuring shear thickening,and particles make contacts even at the first shear thinning conditions.The second normal stress difference exhibit similar evolution with viscosity while the first normal stress difference is mainly dominated by fluctuations.Microstructure analy-sis shows frictional clusters appear in repulsive suspensions with growth in both quantity and size as shear rate increases.Clusters in strongly adhesive suspensions,on the other hand,break into smaller ones,resulting in a viscosity reduction.The calculation of the shape anisotropy indicates that frictional clusters in repulsive suspensions tend to expand uniformly in simulation box whereas at high attractive strength,clusters deform more cylindrical when strongly sheared.Our studies in microstructure can fundamentally
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