Simultaneous Image Measurements of Velocity Field and Water-Surface Wave in Open-Channel Flows
Simultaneous Image Measurements of Velocity Field and Water-Surface Wave in Open-Channel Flows
复制标题
明渠流中速度场和水面波的同步图像测量
DOI：
10.1061/40655(2002)87
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
T. Kanda
中科院分区：
文献类型：
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作者：
H. Miyamoto;T. Kanda
在本文中，我们提出了一种图像处理技术，同时测量瞬时速度矢量和相应的水面线在明渠流。该技术利用图像，其中流动水中的示踪粒子和水面轮廓都通过激光片可视化。采用图像亮度梯度矢量和两个阈值提取图像边界的边界检测算法，对图像进行处理，识别空气-水界面。将该算法与粒子图像测速技术（PIV）相结合，可以同时测量水面高度和速度矢量。这种新开发的测量技术，然后使用超临界明渠流凹床的目的是检查其适用性的快速流动与强烈的水面波动。瞬时测量的水面高度和流速矢量数据集提供了大量关于水面波动的水流动力学信息。通过对平均流速、平均水面和紊动量的分析表明：（1）在凹口上游区域，由剪切不稳定引起的流速脉动在主槽和凹口之间占主导地位;（2）混合剪切层在中下游区域发展，（3）流速脉动与有组织运动和水面脉动有很好的相关性，特别是在下游区域。时空相关分析表明，混合剪切层中的有组织运动与水面脉动有很强的相互作用。这些结果有力地证实了本技术是非常有用的快速流动与显着波动的水面检查。
In the present paper, we propose an image processing technique for simultaneously measuring instantaneous velocity vectors and the corresponding water-surface profile in an open-channel flow. This technique utilizes images in which both the tracer particles in the flowing water and the water-surface profile are visualized by a laser light sheet. A boundary-detecting algorithm, in which gradient vectors of the image luminance and two thresholds are used for extracting image boundaries, is employed in the image processing for identifying the air-water interface. Combining this algorithm with a particle image velocimetry (PIV) allows us to simultaneously measure the water-surface heights and the velocity vectors. This newly developed measuring technique is then used to a supercritical open-channel flow over a concaved bed for the purpose of examining its applicability to rapid flows with strong water-surface fluctuations. Instantaneously measured data sets of water-surface heights and flow velocity vectors provide a lot of information on the flow dynamics with water-surface fluctuations. Analyses of the mean velocity, mean water surface and turbulent quantities show that (1) in the upstream region of the concave, the velocity fluctuations generated by shear instability are dominant between the main-channel and the concave, (2) the mixing shear layer develops in the middle to downstream regions, and (3) the velocity fluctuations are well correlated to the organized motions as well as the water-surface fluctuations especially in the downstream region. The space-time correlation analysis suggests that there is a strong interaction between the water-surface fluctuation and the organized motion in the mixing shear layer. It is strongly confirm from these results that the present technique is very useful in examination of rapid flows with significantly fluctuating water-surface.