Image processing techniques for the measurement of two-phase bubbly pipe flows using particle image and tracking velocimetry (PIV/PTV)
Image processing techniques for the measurement of two-phase bubbly pipe flows using particle image and tracking velocimetry (PIV/PTV)
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DOI：
10.1016/j.ces.2018.05.029
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发表时间：
2018-11-02
影响因子：
4.7
通讯作者：
Maliska, C. R.
中科院分区：
文献类型：
--
作者：
Cerqueira, R. F. L.;Paladino, E. E.;Maliska, C. R.
气液两相泡状流的粒子图像测速技术（PIV）测量是一项具有挑战性的工作，主要是由于气液界面引起的激光色散。所采用的常见解决方案是使用与用于激光的带通滤波器相关联的荧光播种颗粒。因此，相机仅捕获由接种颗粒发出荧光的光，过滤由气-液界面分散的激光，并测量对应于接种有颗粒的液相的速度场。然而，即使对于相对较低的气体分数，由界面反射的荧光也会使测量失真，因为它将颗粒从激光平面照射出来。此外，荧光也反映在界面处，扭曲的测量和倾向于过冲测量的液体速度在这项工作中，PIV测量的空气-水泡状流在一个小直径的管道（D = 26.2 mm）进行荧光示踪粒子（PIV/LIF）。针对PIV技术中存在气泡的问题，提出了一种新的相位判别方法，该方法利用每个询问窗口的像素强度信息来判别该窗口是液体区域还是气泡区域。为了验证的PIV程序，粒子跟踪测速（PTV）算法也被开发来测量气泡的速度，在文献中发现的类似的实现的基础上，但也提出了一些修正，以克服气泡重叠现象，出现在气泡管流，当使用后向照明。通过一系列不同含气率和气泡直径的实验，对PIV和PTV方法进行了测试和验证，证实了两种方法的准确性和可靠性。所提出的方法被用来分析一组向上的层流和湍流泡状流，平均轴向速度和分散的气泡修改的湍流强度分布。(C)2018爱思唯尔有限公司版权所有。
Particle Image Velocimetry (PIV) measurement in gas-liquid bubbly flows is a challenging task, mainly due to the dispersion of the laser light caused by the gas-liquid interfaces. A common solution adopted is the use of fluorescent seeding particles associated with a bandpass filter for the laser light. Therefore, the camera captures only the light fluoresced by the seeding particles, filtering the laser light dispersed by the gas-liquid interfaces and measuring a velocity field which corresponds to the liquid phase, seeded with the particles. However, even for relatively low gas fractions, the fluoresced light reflected by the interfaces distorts the measurements, as it illuminates particles out from the laser plane. In addition, the fluoresced light also reflects at the interfaces, distorting the measurements and trending to overshoot the measured liquid velocities In this work, PIV measurements of air-water bubbly flows in a small diameter pipe (D = 26.2 mm) are performed with fluorescent tracer particles (PIV/LIF). A new method for the phase discrimination in PIV was developed to overcome the problems caused by the presence of bubbles in the flow, which uses the pixels intensity information of each interrogation window, to identify if that window corresponds to liquid or bubble region. To validate the PIV procedure, a Particle Tracking Velocimetry (PTV) algorithm was also developed to measure the bubbles velocities, based on similar implementations found in literature, but some corrections were also proposed to overcome the bubble overlap phenomena which arises in bubbly pipe flows, when backward illumination is used. The PIV and the PTV methods were tested and validated by a series of distinct gas void fraction and bubble diameters experimental cases, confirming the accuracy and reliability of both methods. The proposed method was used to analyze a set of upward laminar and turbulent bubbly flows, showing that the averaged axial velocity and the dispersed gas bubbles modify the turbulence intensity profiles. (C) 2018 Elsevier Ltd. All rights reserved.