Bubbly flow widely exists in many industrial applications of energy, metallurgy, and chemistry, etc. Due to the clusters and overlap of dense bubbles at a high void fraction, it is nearly impossible to obtain the information of flow structures and characteristics in the spatial field with traditional measurement methods. In this paper, a novel laser scanning based 3-D reconstruction method for dense bubbly plume is developed. The measurement area is scanned by a laser sheet through a rotating hexagonal optical prism, and a high-speed camera captures the sequentially sliced images in the flow field, which is parallel to the scanning direction. Meanwhile, a scanning mathematic model is established, and its linearization is analyzed in detail. An image preprocessing method is developed to extract the features of the bubbly plume. To be specific, a method involves adaptive wavelet threshold denoising is developed to remove the noise. Moreover, methods regarding sliced image-matching and interpolation based on Log-polar transformation are presented to improve the spatial resolution effectively, and a set of image evaluation standards are designed to investigate the interpolation efficiency and accuracy. The experimental results conclude that the reported 3-D reconstruction method for dense bubbly flow based on laser scanning is valid with high precision, which explores a new way for the visualization of the 3-D structures and measurement of the volumetric flow field and the complex flow characteristics.

中文翻译：

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一种基于激光扫描的密集气泡羽流三维重建方法

气泡流广泛存在于能源、冶金、化工等诸多工业应用中。 由于高空隙率下致密气泡的聚集和重叠，几乎不可能获得空间场中流动结构和特征的信息用传统的测量方法。在本文中，开发了一种新的基于激光扫描的 3-D 重建密集气泡羽流的方法。测量区域由激光片通过旋转的六边形光学棱镜进行扫描，高速摄像机在平行于扫描方向的流场中捕捉依次切片的图像。同时，建立了扫描数学模型，并对其线性化进行了详细分析。开发了一种图像预处理方法来提取气泡羽流的特征。再具体一点，开发了一种涉及自适应小波阈值去噪的方法来去除噪声。此外，提出了基于对数极坐标变换的切片图像匹配和插值方法，以有效提高空间分辨率，并设计了一套图像评估标准来考察插值效率和精度。实验结果表明，所报道的基于激光扫描的稠密气泡流 3-D 重建方法是有效且精度高的，为 3-D 结构的可视化和体积流场的测量以及复杂流场的测量探索了一种新方法。流动特性。提出了基于对数极坐标变换的切片图像匹配和插值方法，以有效提高空间分辨率，并设计了一套图像评价标准，考察插值效率和精度。实验结果表明，所报道的基于激光扫描的稠密气泡流 3-D 重建方法是有效且精度高的，为 3-D 结构的可视化和体积流场的测量以及复杂流场的测量探索了一种新方法。流动特性。提出了基于对数极坐标变换的切片图像匹配和插值方法，以有效提高空间分辨率，并设计了一套图像评价标准，考察插值效率和精度。实验结果表明，所报道的基于激光扫描的稠密气泡流 3-D 重建方法是有效且精度高的，为 3-D 结构的可视化和体积流场的测量以及复杂流场的测量探索了一种新方法。流动特性。