Lappan Tobias, Franz Alexander, Schwab Holger, Kühn Uta, Eckert Sven, Eckert Kerstin, Heitkam Sascha
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Fluid Dynamics, 01328 Dresden, Germany.
Technische Universität Dresden, Institute of Process Engineering and Environmental Technology, 01062 Dresden, Germany.
Soft Matter. 2020 Feb 26;16(8):2093-2103. doi: 10.1039/c9sm02140j.
In this work, we introduce a novel approach to measure the flow velocity of liquid foam by tracking custom-tailored 3D-printed tracers in X-ray radiography. In contrast to optical observations of foam flow in flat cells, the measurement depth equals 100 mm in the X-ray beam direction. Light-weight tracers of millimetric size and tetrapod-inspired shape are additively manufactured from stainless steel powder by selective laser melting. Matching with the foam structure and bubble size, these tracers follow the foam flow. An X-ray beam passes through the radiotransparent foam channel and is detected by an X-ray image intensifier. The X-ray transmission images show the two-dimensional projections of the radiopaque tracers. Utilizing particle tracking velocimetry algorithms, the tracer trajectories are measured with both high spatial (0.2 mm) and temporal (25 fps) resolution. Fine and coarse liquid foam flow of different velocities are studied in a partly curved channel with rectangular cross section. The simultaneous time-resolved measurements of the tracers' translational motion and their intrinsic rotation reveal both the local velocity and vorticity of the foam flow. In the semi-circular curved channel section, the rigid-body-like flow pattern is investigated. Moreover, a relaxation of the foam structure in the transition zone between straight and curved section is observed.
在这项工作中，我们介绍了一种通过在X射线成像中跟踪定制的3D打印示踪剂来测量液体泡沫流速的新方法。与在扁平单元中对泡沫流动进行光学观察不同，在X射线束方向上测量深度为100毫米。毫米尺寸且受四足动物启发形状的轻质示踪剂通过选择性激光熔化由不锈钢粉末增材制造而成。这些示踪剂与泡沫结构和气泡尺寸相匹配，跟随泡沫流动。一束X射线穿过射线可透过的泡沫通道，并由X射线图像增强器进行检测。X射线透射图像显示了不透射线示踪剂的二维投影。利用粒子跟踪测速算法，以高空间分辨率（0.2毫米）和时间分辨率（25帧/秒）测量示踪剂轨迹。在具有矩形横截面的部分弯曲通道中研究了不同速度的细泡沫流和粗泡沫流。对示踪剂平移运动及其固有旋转的同时时间分辨测量揭示了泡沫流动的局部速度和涡度。在半圆形弯曲通道部分，研究了类似刚体的流动模式。此外，观察到在直段和弯曲段之间的过渡区域中泡沫结构的松弛现象。
