We examine the dynamics of small anisotropic particles (spheroids) sedimenting through homogeneous isotropic turbulence using direct numerical simulations and theory. The gravity-induced inertial torque acting on sub-Kolmogorov spheroids leads to pronouncedly non-Gaussian orientation distributions localized about the broadside-on (to gravity) orientation. Orientation distributions and average settling velocities are obtained over a wide range of spheroid aspect ratios, Stokes, and Froude numbers. Orientational moments from the simulations compare well with analytical predictions in the inertialess rapid-settling limit, with both exhibiting a nonmonotonic dependence on spheroid aspect ratio. Deviations arise at Stokes numbers of order unity due to a spatially inhomogeneous particle concentration field resulting from a preferential sweeping effect; as a consequence, the time-averaged particle settling velocities exceed the orientationally averaged estimates.

中文翻译：

---

湍流中沉积各向异性颗粒的取向动力学

我们使用直接数值模拟和理论研究了通过均质各向同性湍流沉降的各向异性小颗粒（球体）的动力学。作用在子Kolmogorov椭球上的重力感应惯性扭矩会导致明显的非高斯定向分布，该分布分布在宽边指向（重力）方向上。可以在很大的球体长宽比，斯托克斯数和弗洛德数范围内获得取向分布和平均沉降速度。来自模拟的定向力矩与无惯性快速沉降极限中的分析预测相比较，两者均显示出对球体纵横比的非单调依赖性。由于优先扫掠效应导致的空间不均匀粒子浓度场，斯托克斯数阶单位出现偏差。