Data associated with "Settling dynamics of two identical vertical aligned spheres in a thixotropic fluid."

Despite the great relevance of particle dynamics in non-Newtonian fluids, particles settling in non-Newtonian fluids has received limited scientific attention. The simple case of two vertically aligned spheres settling in a thixotropic xanthan fluid is considered using solutions of xanthan + glycerol + water and 0.75 mm radius stainless steel spheres. Chaining phenomenon is observed where the trailing sphere velocity is increased due to a corridor of reduced viscosity created by the leading sphere. Our experimental methods are first validated against a Newtonian fluid of glycerol + water in which the sphere velocities remained equal. Using the fluid velocity induced by a single sphere, the two sphere velocities are approximated by Faxén’s first law. In a non-Newtonian (thixotropic) xanthan fluid, a viscosity ratio is introduced to account for the reduced fluid viscosity encountered by the trailing sphere due to the slow structure recovery after shear thinning. The viscosity ratio is an exponential decay function dependent on the time between spheres normalised by the fluid recovery time, a parameter which is experimentally determined. When the sphere-sphere separation is large, the viscosity ratio tends towards unity. The predicted settling velocities show good agreement with experimental data.

尽管非牛顿流体中的颗粒动力学具有重要的研究意义，但针对非牛顿流体中颗粒沉降现象的科学研究仍有待进一步深化。本研究聚焦于两相竖直排列球体在触变性黄原胶流体中的沉降这一简化场景，实验采用黄原胶+甘油+水配制的混合溶液作为流体介质，并使用半径为0.75 mm的不锈钢球体作为沉降颗粒。实验中观测到链化现象：领先球体经剪切作用形成低黏度通道，使得尾随球体的沉降速度得以提升。本研究首先以甘油+水配制的牛顿流体作为对照体系验证实验方法的可靠性，该体系中两相球体的沉降速度保持一致。基于单球体诱导产生的流场速度，研究采用法森第一定律（Faxén’s first law）对两相球体的沉降速度进行近似计算。针对非牛顿（触变性）黄原胶流体，本研究引入黏度比参数，以修正尾随球体因剪切变稀后流体结构缓慢恢复而遭遇的局部黏度降低效应。该黏度比为指数衰减函数，其自变量为球体间的时间间隔经流体恢复时间归一化后的结果，其中流体恢复时间为实验测定的参数。当球体间距较大时，黏度比趋近于1。最终预测得到的沉降速度与实验数据吻合良好。