Experimental study for stratified flow around an impulsively started rotating cylinder using combined PIV and LIF

使用 PIV 和 LIF 相结合的脉冲启动旋转圆柱体周围分层流的实验研究

基本信息

批准号：
18560183
负责人：
FUKUSHIMA Chiharu
金额：
$ 2.36万
依托单位：
Hiroshima 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：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

项目摘要

An experimental study has conducted for density-stratified circular flow induced by an impulsively started rotating cylinder. The objective of the present study is qualitative classification of visualized flow pattern and understanding of relationship between the variation of velocity field and that of density field. To achieve them, several experimental techniques, such as electrolytic precipitation and dye injection method, laser induced fluorescent (LIF), particle image velocimetry (PIV), and shadowgraph, are employed. The Reynolds number (Re=r^<2>ω)/v=100-300, where r is radius and ω angular velocity of rotating cylinder) and the Froude number (Fr=ω/N=4-12, N is buoyancy frequency) are varied independently. At the beginning of the rotation, instability of dyed flow pattern becomes significant, and then rolls up the mushroom-type vortex ring array. The evolutions of dyed vortex pattern lead to subsequent large-scale layered formation. During the layered formation and the rearrangement of the flow pattern, the dyed flow exhibits the behavior of oscillating motion. The vorticity contours show the corresponding occurrence of vortex ring array around the cylinder. In addition, occurrence of pairs of vorticity array nearby the cylinder is observed even in the situation where the large-scale layered formation is maintained. The oscillating dyed flow motion far from the cylinder, therefore, is due to the occurrence of vorticity nearby the cylinder. The Reynolds number and the Froude number affected the radial length scale of the layered formation, while the wavelength was almost independent of Reynolds number. The density field exhibits corresponding variations with those of dyed flow pattern and the vorticity within certain time period. However, variations of density gradient become negligible with time progress, while the remarkable layered motion of dyed pattern is still observed. It means that the significant time scale exists in the present mixing phenomenon.

进行了一项实验研究，该研究是针对脉冲开始旋转圆柱体诱导的密度分离的圆流。本研究的目的是可视化流程模式的质量分类以及对速度场和密度场变化之间关系的理解。为了实现它们，采用了几种实验技术，例如电解沉淀和染料注射方法，激光诱导的荧光（LIF），粒子图像速率（PIV）和阴影图。雷诺数（re = r^<2>ω）/v = 100-300，其中r是半径，旋转缸的角速度）和弗洛德号（FR =ω/n = 4-12，n是浮力频率）是独立的。在旋转开始时，染色流动模式的不稳定性变得显着，然后将肌肉型涡流环阵列卷起。染色涡流模式的进化导致随后的序列大规模分层形成。在分层的形成和流动模式的重排期间，染色的流动表现出振荡运动的行为。涡度轮廓显示了圆柱体周围的涡流阵列的相应出现。另外，即使在保持大规模分层形成的情况下，也观察到圆柱附近的涡度阵列对。因此，远离气缸的振荡染色流动运动是由于雷诺数和弗洛德数量影响了分层形成的径向长度尺度，而波长几乎与雷诺数无关。密度场在特定时间段内表现出与染色流动模式和涡度的相应变化。但是，密度梯度的变化随时间进度而言可以忽略不计，而染色模式的显着分层运动仍被观察到。这意味着在当前的混合现象中存在重要的时间尺度。