Abstract:

The light field particle tracking velocimetry (PTV) can track the trajectories of the bubbles in the gas-liquid two-phase flow via a single camera. This method provide a solution for the measurement of bubble parameters in space-constraint applications. However, under the conditions of high bubble concentration and large bubble displacement, the matching accuracy of PTV bubbles in the light field is low, resulting in significant velocity measurement errors. In order to solve this problem, this paper proposed a bubble matching method based on global position iteration and polar coordinate system similar technology (GPPI-PCSS). The GPPI-PCSS method iteratively updated the positions of all bubbles in a single frame image through the three-dimensional displacement field obtained by the PCSS matching method. As a result, the bubble positions in the two frames gradually coincide and the accurate bubble matching results could be obtained. The performance of the GPPI-PCSS method was evaluated by experimental study of the bubble motion behavior in the bubbling bed through light field PTV. Results showed that the average bubble matching accuracy of the GPPI-PCSS method was 92.65% in the range of 0.5—7ms sampling interval and 0.15—0.35L/min air flow, which was higher than 81.38% of the traditional PCSS method and 84.12% of the relaxation method, respectively. In addition, the maximum motion velocity of bubbles measured by GPPI-PCSS method ranged from 38.34—49.87cm/s, which was consistent with the theoretical calculation value. These results indicate that the proposed GPPI-PCSS method could be used in light-field PTV technology to obtain accurate bubble velocity measurement results under the conditions of high bubble concentration and large bubble displacement.

Key words: light field imaging, particle tracking velocimetry (PTV), bubble matching, polar coordinate system similar algorithm, global location iteration

摘要：

光场粒子跟踪测速（PTV）技术能够在单视角条件下重建气液两相流中气泡的三维空间位置，实现气泡运动轨迹的跟踪，为受限空间条件下气泡参数测量提供了解决方案。然而，在气泡浓度较高以及位移量较大的条件下，光场PTV气泡匹配准确率较低，由此导致气泡运动速度场测量结果出现明显的错误矢量。为解决该问题，本文提出了基于全局位置迭代以及极坐标系统相似技术的气泡匹配方法（GPPI-PCSS），通过PCSS匹配方法所获得的气泡三维速度场对单帧图像内所有气泡的位置进行迭代更新，使两帧图像中的气泡位置逐渐重合，由此获得高准确度的气泡匹配结果。通过开展鼓泡床内气泡运动行为光场PTV实验研究，对GPPI-PCSS方法的准确性进行了评价。结果表明：在采样间隔0.5~7ms、空气流量0.15~0.35L/min工况范围内，GPPI-PCSS方法的气泡匹配准确率的平均值为92.65%，分别高于传统PCSS方法的81.38%和松弛方法的84.12%。此外，通过GPPI-PCSS方法所测量得到的气泡最大运动速度范围为38.34~49.87cm/s，与理论计算值一致，由此证明了所提出的GPPI-PCSS方法可以用于光场PTV技术中，在高气泡浓度、大气泡位移条件下获得准确的气泡速度测量结果。

关键词: 光场成像, 粒子跟踪测速, 气泡位置匹配, 极坐标系统相似技术, 全局位置迭代