Numerical simulations of a sphere settling through a suspension of neutrally buoyant fibres
Numerical simulations of a sphere settling through a suspension of neutrally buoyant fibres
复制标题
球体通过中性浮力纤维悬浮液沉降的数值模拟
作者：
O. Harlen;R. R. Sundararajakumar;D. Koch
通过悬浮液的中性浮力纤维的一个小的致密球体的沉降研究通过数值模拟技术，包括纤维-纤维接触力和远程流体动力学相互作用。在球体直径小于纤维长度的情况下，排除纤维之间接触影响的计算严重低估了实验中测得的球体上的拖曳力。通过在我们的模拟中包括纤维-纤维接触，我们能够解释这种差异，以及阻力对纤维初始取向的强烈依赖性。在低和中等值的nL3，其中n是每单位体积的纤维的数量和L的纤维长度，流体动力学的相互作用被发现是重要的，在缓和纤维之间的接触的效果。当球体直径远小于纤维长度和纤维间距，但大的纤维厚度相比，极限的渐近解。这被发现是在良好的协议与模拟。通过一个单层的纤维沉降的计算结果也被提出，作为一个模型的半浓缩悬浮液。由于几何限制，纤维之间的碰撞更加频繁。
The sedimentation of a small dense sphere through a suspension of neutrally buoyant fibres is investigated via a numerical simulation technique that includes both fibre–fibre contact forces and long-range hydrodynamic interactions. In situations where the diameter of the sphere is smaller than the length of the fibres, calculations that exclude the effect of contacts between fibres severely underestimate the drag force on the sphere measured in experiments. By including fibre–fibre contacts in our simulations we are to able to account for this discrepancy, and also the strong dependence of the drag on the initial orientation of the fibres. At low and moderate values of nL3, where n is the number of fibres per unit volume and L the fibre length, hydrodynamic interactions are found to be important in moderating the effect of contacts between fibres. An asymptotic solution is presented for the limit when the sphere diameter is much smaller than both the fibre length and inter-fibre spacing, but large compared to the fibre thickness. This is found to be in good agreement with the simulations. Results of calculations on sedimentation through a monolayer of fibres are also presented, as a model of a semi-concentrated suspension. Collisions between fibres are much more frequent, due to the geometric confinement.