Understanding particle drift in suspension flows is of the highest importance in numerous engineering applications where particles need to be separated and filtered out from the suspending fluid. Commonly known drift mechanisms such as the Magnus force, Saffman force and Segré–Silberberg effect all arise only due to inertia of the fluid, with similar effects on all non-spherical particle shapes. In this work, we present a new shape-selective lateral drift mechanism, arising from particle inertia rather than fluid inertia, for ellipsoidal particles in a parabolic velocity profile. We show that the new drift is caused by an intermittent tumbling rotational motion in the local shear flow together with translational inertia of the particle, while rotational inertia is negligible. We find that the drift is maximal when particle inertial forces are of approximately the same order of magnitude as viscous forces, and that both extremely light and extremely heavy particles have negligible drift. Furthermore, since tumbling motion is not a stable rotational state for inertial oblate spheroids (nor for spheres), this new drift only applies to prolate spheroids or tri-axial ellipsoids. Finally, the drift is compared with the effect of gravity acting in the directions parallel and normal to the flow. The new drift mechanism is stronger than gravitational effects as long as gravity is less than a critical value. The critical gravity is highest (i.e. the new drift mechanism dominates over gravitationally induced drift mechanisms) when gravity acts parallel to the flow and the particles are small.

中文翻译：

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抛物线速度剖面导致惯性椭球的形状选择性漂移

在许多需要从悬浮液中分离和过滤掉颗粒的工程应用中，了解悬浮液中的颗粒漂移是最重要的。众所周知的漂移机制，如马格努斯力、萨夫曼力和 Segré-Silberberg 效应都只是由于流体的惯性而产生的，对所有非球形颗粒形状都有类似的影响。在这项工作中，我们提出了一种新的形状选择性横向漂移机制，由粒子惯性而非流体惯性产生，用于抛物线速度剖面中的椭圆体粒子。我们表明，新的漂移是由局部剪切流中的间歇性翻滚旋转运动以及粒子的平移惯性引起的，而旋转惯性可以忽略不计。我们发现，当粒子惯性力与粘性力的数量级大致相同时，漂移最大，并且极轻和极重粒子的漂移都可以忽略不计。此外，由于翻滚运动对于惯性扁球体（也不是球体）不是稳定的旋转状态，因此这种新的漂移仅适用于长球体或三轴椭球。最后，将漂移与在平行和垂直于流动的方向上作用的重力效应进行比较。只要重力小于临界值，新的漂移机制就比重力效应强。当重力平行于流动且颗粒较小时，临界重力最高（即新的漂移机制优于重力诱导的漂移机制）。