Settling of inertial nonspherical particles in wavy flow
Settling of inertial nonspherical particles in wavy flow
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DOI：
10.1103/physrevfluids.5.124301
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发表时间：
2020-12-04
影响因子：
2.7
通讯作者：
Koseff, Jeffrey R.
中科院分区：
文献类型：
--
作者：
Clark, Laura K.;DiBenedetto, Michelle H.;Koseff, Jeffrey R.
微塑料是世界海洋中一个日益严重的问题。它们通过各种海洋现象进行传输，其中最基本的现象之一是表面重力波。由于微塑料形状不规则且通常不是中性浮力的，因此了解负浮力、非球形塑料颗粒在表面重力波作用下的沉降对于准确预测海洋中微塑料的命运至关重要。在此，我们通过实验研究了塑料棒、圆盘和球体在波浪流中的沉降情况。我们发现，相对于静止流中的颗粒沉降速度，颗粒在波浪中的平均垂直速度可能增加也可能降低。这种变化是颗粒长度尺度上的流动惯性的函数，我们用颗粒雷诺数Re - p来表征它，同时也是颗粒形状的函数。我们通过考察影响其行为的两个因素进一步研究了颗粒的平均垂直速度：颗粒与流体之间的相对速度以及颗粒对流体的采样方式。我们发现，即使棒体的相对速度随方向的变化随着Re - p的增加而增加，颗粒与流体之间的平均相对速度也随Re - p保持不变。观察到的平均垂直颗粒速度随Re - p的变化可以通过颗粒对流体的采样方式来解释，因为每种颗粒形状作为Re - p的函数对流体的采样都是不均匀的。在模型中考虑颗粒沉降速度随形状和惯性的变化对于提高海洋中微塑料传输预测的准确性是必要的。
Microplastics are an increasingly significant problem in the world's oceans. They are transported by various ocean phenomena, one of the most fundamental of which is surface gravity waves. Since microplastics are irregularly shaped and are not typically neutrally buoyant, understanding the settling of negatively buoyant, nonspherical plastic particles under surface gravity waves is important for accurately predicting the fate of microplastics in the ocean. Here we experimentally investigate the settling of plastic rods, disks, and spheres in wavy flows. We find that the average vertical velocities of the particles can both increase and decrease in waves, relative to the particle settling velocity in quiescent flow. This variation is a function of the flow inertia at the length scale of the particle, which we characterize with a particle Reynolds number, Re-p, and is also a function of particle shape. We further examine the average vertical particle velocities by looking at two factors contributing to their behavior: The relative velocities between the particles and the flow and the manner in which the particles sample the flow. We find that the average relative velocities between the particles and the flow remain constant with Re-p, even though the variation of the relative velocities of the rods with orientation increases with increasing Re-p. The observed variation of the average vertical particle velocities with Re-p can be explained instead by how the particles sample the flow, as each of the particle shapes nonuniformly sample the flow as a function of Re-p. Accounting for the variation of particle settling velocities with shape and inertia in models is necessary to improve the accuracy of predictions of the transport of microplastics in the ocean.