论文标题

静态液体和湍流中细弯曲颗粒的沉降行为

Settling behaviour of thin curved particles in quiescent fluid and turbulence

论文作者

Chan, Timothy T. K., Esteban, Luis Blay, Huisman, Sander G., Shrimpton, John S., Ganapathisubramani, Bharathram

论文摘要

薄弯曲掉落颗粒的运动在自然和工业上都是无处不在的,但尚未得到广泛检查。在这里,我们描述了一项关于薄圆柱形壳的动力学的实验研究,类似于通过静止的液体和均质各向异性湍流沉降的破碎瓶碎片。粒子具有基于平均下降速度$ 0.75 \ times 10^4 \ Lessim ar \ Lessim 2.75 \ times 10^4 $的Archimedes数字。湍流使用安装在共同平面配置中的随机喷射阵列在水箱中生成$re_λ\ $re_λ\的数量。流动在统计上固定后,释放粒子,并使用两个正交定位的高速摄像机记录其三维运动。我们提出了一个简单的摆模型,该模型可以准确地捕获静态流体中颗粒的速度波动,并发现掉落样式的差异可以通过粒子的螺距角度与其速度向量之间的紧密比对来解释。通过将背景湍流下的轨迹与静态流体情况进行比较,我们测量了测试条件的湍流中平均下降速度的降低。我们还研究了颗粒的二次运动,并确定了湍流所独有的下降事件,例如“长滑行”和“快速旋转”事件。最后,我们显示出背景湍流下颗粒的径向分散体的增加,并将下降事件的时间尺度与局部沉降速度相关联。

The motion of thin curved falling particles is ubiquitous in both nature and industry but is not yet widely examined. Here, we describe an experimental study on the dynamics of thin cylindrical shells resembling broken bottle fragments settling through quiescent fluid and homogeneous anisotropic turbulence. The particles have Archimedes numbers based on the mean descent velocity $0.75 \times 10^4 \lesssim Ar \lesssim 2.75 \times 10^4$. Turbulence reaching a Reynolds number of $Re_λ\approx 100$ is generated in a water tank using random jet arrays mounted in a co-planar configuration. After the flow becomes statistically stationary, a particle is released and its three-dimensional motion is recorded using two orthogonally positioned high-speed cameras. We propose a simple pendulum model that accurately captures the velocity fluctuations of the particles in still fluid and find that differences in the falling style might be explained by a closer alignment between the particle's pitch angle and its velocity vector. By comparing the trajectories under background turbulence with the quiescent fluid cases, we measure a decrease in the mean descent velocity in turbulence for the conditions tested. We also study the secondary motion of the particles and identify descent events that are unique to turbulence such as 'long gliding' and 'rapid rotation' events. Lastly, we show an increase in the radial dispersion of the particles under background turbulence and correlate the timescale of descent events with the local settling velocity.

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