The sedimentation of a suspension of rigid spherical particles in a polymeric fluid is studied employing experiments and particle-resolved numerical simulations. It is shown that the settling process in a viscoelastic Boger fluid is time-dependent and inhomogeneous; both experiments and simulations exhibit the formation of particle-rich, fast-settling regions and particle-depleted regions with backflow. The settling process in a Newtonian fluid is investigated for comparison, and is shown to be homogeneous, with velocity fluctuations that decay following random mixing. In the viscoelastic Boger fluid, the mean settling rate is higher than that measured in a similar Newtonian suspending fluid, and in our experiments, higher than that of a single particle settling in isolation. When a cross shear flow is imposed, the mean settling rate in the viscoelastic Boger fluid is drastically reduced; the magnitude of the reduction is greater than that measured for a single particle, suggesting that both fluid elasticity and the suspension’s particle volume fraction have important effects.

中文翻译：

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粘弹性流体中颗粒沉降的集体效应

使用实验和颗粒分解数值模拟研究了刚性球形颗粒在聚合物流体中的悬浮液的沉积。结果表明，在粘弹性的Boger流体中的沉降过程是随时间变化且不均匀的。实验和模拟都显示了富颗粒，快速沉降区域和带逆流的颗粒耗尽区域的形成。对牛顿流体中的沉降过程进行了比较研究，结果表明该过程是均匀的，其速度波动随随机混合而衰减。在粘弹性的Boger流体中，平均沉降速率要高于在类似的牛顿悬浮液中测得的沉降速率，而在我们的实验中，其平均沉降速率要高于单独分离的单个粒子的沉降速率。当施加横切流时，粘弹性Boger流体的平均沉降速度大大降低；减小的幅度大于单个颗粒的减小幅度，表明流体弹性和悬浮液的颗粒体积分数均具有重要影响。