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.

测量了通过均匀和各向同性湍流掉落颗粒的速度，以研究湍流对小颗粒运动的影响，这对湍流几乎没有影响。在我们的实验室中开发的盒螺旋脉冲发生器中产生了异位和均匀的湍流。矩形盒中安装了四个反向旋转网格。通过快速旋转，在网格之间实现了各向同性和均匀的湍流，并实现了零均值的流动。 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.研究中使用了两种类型的粒子（PMMA和实心玻璃）。粒子的尺寸为100μm，比Kolmogorov尺度或湍流的最小尺度小得多。因此，假定粒子周围的流量是均匀的。通过改变湍流的强度，控制粒子对湍流时间尺度的空气动力响应时间，并检查了降落速度的平均速度的增加/减小。过去的研究报告说，订单统一时间比率下降速度下降的最大增加。但是，观察到固体玻璃颗粒（最大减少2％），而PMMA颗粒相同的趋势（最大增加15％）的趋势。发现时间尺度比不是确定湍流对粒子运动的影响的独特因素。因此，对过去DNS研究的湍流对粒子运动的影响进行建模需要谨慎。我们将继续进行当前的研究，以寻求另一个因素来控制湍流中的粒子运动。