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Experimental study on effect of turbulent structure on small falling air-borne particle.

湍流结构对空中小颗粒下落影响的实验研究

基本信息

批准号：
17560144
负责人：
USHIJIMA Tatsuo
金额：
$ 2.24万
依托单位：
Nagoya Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2006
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-17560144/
关键词：
Turbulence Multiphase Flow Terminal velocity Stokes number 乱入流体力学

项目摘要

Velocity of falling particle through homogenous and isotropic turbulence was measured to study the effect of turbulence on motion of small particle, which has little influence on turbulence.Isotropic and homogeneous turbulence was generated in box-turbulence generator that had been developed in our laboratory. Four counter-rotating grids are installed in a rectangular box. By rapid rotation, isotropic and homogeneous turbulence with zero-mean flow was realized between grids. Particles are dropped in a turbulent velocity field and were recorded by high-speed camera and the image was analyzed by Particle Tracking Velocimetry (PTV) to estimate the velocity of the falling particles.Varying the intensity of turbulence, we measured the mean velocity of falling particles, which are compared with the terminal velocity of particle, and investigate the effect of the turbulence. Two types of particle (PMMA and solid glass) are used in the study. The size of particle is 100 μm and much smaller than the Kolmogorov scale or the smallest scale of the turbulence. It is, therefore, assumed that the flow around particle is uniform. By varying the intensity of the turbulence, the aerodynamic response time of particle to the turbulent time scale are controlled and the increase/decrease in the mean velocity of falling velocity are examined. The past research reported the maximum increase of the falling velocity for the time ratio of order unity. However, the reversed trend is observed for the solid glass particles (2% decrease at maximum) while the same trend (15% increase at maximum) for the PMMA particles.It is found that the time scale ratio is not the unique factor to determine the effect of turbulence on particle motion. Therefore, modelling of the effect of turbulence on particle motion from the past DNS research needs some caution. We shall continue the current research, seeking for another factor to control the particle motion in a turbulent flow.

测量下落颗粒通过均匀各向同性湍流的速度，研究湍流对小颗粒运动的影响，对湍流影响较小。各向同性均匀湍流是在本实验室研制的箱式湍流发生器中产生的。四个反向旋转的栅格安装在一个矩形盒子内。通过快速旋转，网格间实现了各向同性、均匀的零均流湍流。颗粒落在湍流速度场中，并用高速摄像机记录下来，并通过粒子跟踪测速（PTV）分析图像来估计下落颗粒的速度。通过改变湍流强度，我们测量了下落颗粒的平均速度，并将其与颗粒的终端速度进行比较，并研究了湍流的影响。研究中使用了两种类型的颗粒（PMMA 和固体玻璃）。颗粒尺寸为100μm，远小于柯尔莫哥洛夫尺度或湍流的最小尺度。因此，假设颗粒周围的流动是均匀的。通过改变湍流的强度，控制颗粒对湍流时间尺度的空气动力学响应时间，并检查下落速度的平均速度的增加/减少。过去的研究报道了阶次统一的时间比下落速度的最大增加。然而，对于固体玻璃颗粒观察到相反的趋势（最大减少2％），而对于PMMA颗粒观察到相同的趋势（最大增加15％）。发现时间尺度比并不是确定湍流对颗粒运动影响的唯一因素。因此，过去 DNS 研究中湍流对粒子运动影响的建模需要谨慎。我们将继续当前的研究，寻找另一个因素来控制湍流中的粒子运动。