Towards Fluid Dynamics of Foam and Froth

该项目涉及泡沫和泡沫流量的新测量技术的开发和应用。泡沫构成了一种令人着迷的美学材料。同时，它也是一个现代的、跨学科的研究领域。除了科学上的好奇心，固体泡沫还构成了一类新的工程材料。泡沫浮选在选矿过程中起着重要的作用。尽管进行了200年的研究，但泡沫中的许多问题仍然没有解决。特别是对泡沫的流动行为和流体动力学的研究还很少。在牛顿流体中，许多效应，如边界层、热输运或湍流在很大程度上被理解。然而，在泡沫中，这些效应还没有被描述。从本质上讲，这种缺乏研究的原因有两个。首先，泡沫流动要困难得多，受跨越几个长度和时间尺度的许多过程的复杂相互作用所支配。其次，由于泡沫是一种易碎且不透明的相混合物，因此几乎没有合适的测量技术。首先，流动实验采用光学观察接近表面的泡沫运动。它们对泡沫动力学产生了有趣的见解，并显示出与牛顿流体的相当大的偏差。然而，目前还不存在具有合理的时空分辨率的三维调查。同时，数值研究尚未完全建立，缺乏验证实验。在该项目的第一阶段，将开发和验证新的泡沫流量测量技术。在德累斯顿，已经开发了研究液态金属流动的创新技术，其中一些技术在世界范围内是独一无二的。这些技术将适用于泡沫和泡沫。特别是，设想了电阻抗断层摄影术、获得专利的钢丝网传感器、X射线和中子射线摄影术、独特的超快X射线断层摄影术以及用X射线跟踪3D打印示踪剂的技术。初步研究已经证明了其中许多技术对泡沫的适用性。然而，还需要进一步的适应和验证。在项目的第二阶段，将应用测量技术来系统地研究三种常见的泡沫流动：绕圆柱体和后向台阶的流动以及自由射流。通过与牛顿流体的比较，将识别和描述由泡沫的粘弹性、屈服极限以及液体分布、流变学和流体动力学之间的复杂相互作用所引起的独特的影响。大尺度实验的目的是首次观测和分析泡沫流动中的湍流结构。随着该项目的完成，泡沫流动动力学将成为一个新的研究领域。

This project deals with the development and application of novel measurement techniques for foam and froth flow. Foam constitutes an aesthetically fascinating material. At the same time, it is a modern and interdisciplinary field of research. In addition to scientific curiosity solid foams constitute a new class of materials for engineering. The froth flotation plays a major role in mineral processing. Despite 200 years of research many questions in foam remain unsolved. Especially, the flowing behavior and the fluid dynamics of foam are scarcely investigated yet. In Newtonian fluids many effects such as boundary layers, thermal transport or turbulence are understood to a large extend. However, in foam these effects are not yet described. Essentially, there are two reasons for this lack of research. Firstly, foam flow is considerably more difficult, governed by the complex interaction of many processes bridging several length and time scales. Secondly, appropriate measurement techniques scarcely exist because foam poses a fragile and opaque mixture of phases.First flow experiments employ optical observation of the foam movement close to the surface. They yield interesting insights into foam dynamics and demonstrate considerable deviations from Newtonian fluids. However, no three-dimensional investigations with reasonable spatial and temporal resolution exist. At the same time, numerical investigations are not yet fully established and lack validation experiments.In the first phase of the project, novel measurement techniques for foam flow will be developed and validated. In Dresden, innovative techniques for the investigation of liquid metal flow have been developed, some of them unique worldwide. These techniques will be adapted for foam and froth. In particular, Electric impedance tomography, the patented Wire-Mesh sensor, X-ray and neutron radiography, a unique ultrafast X-ray tomography and tracking of 3D-printed tracers with X-ray are envisaged. Preliminary studies have already demonstrated the applicability of many of these techniques to foam. However, further adaption and validation is required.In the second phase of the project, the measurement techniques will be applied in order to investigate systematically three generic foam flows: the flow around a cylinder and over a backward-facing step and the free jet. In that way, the techniques will be validated and a data basis for further validation of experimental and numerical methods will be established.By comparison with Newtonian fluids unique effects will be identified and described, caused by the viscoelasticity, the yield limit, and by the complex interaction between liquid distribution, rheology and fluid dynamics of the foam. Carrying out experiments on large scales aims for the first observation and analysis of turbulent structures in foam flow.By accomplishing the project, foam flow dynamics shall be established as a new field of research.