Towards Fluid Dynamics of Foam and Froth

该项目涉及泡沫和泡沫流的新型测量技术的开发和应用。泡沫构成了一种美学上迷人的材料。同时，它是一个现代和跨学科的研究领域。除了科学好奇心，固体泡沫构成了一种新的工程材料。泡沫浮选在矿物加工中起着重要作用。尽管有200年的研究，泡沫中的许多问题仍然没有解决。 特别是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、热传输或湍流在很大程度上被理解。 然而，在泡沫中，这些影响尚未描述。从本质上讲，缺乏研究有两个原因。首先，泡沫流动是相当困难的，由许多过程的复杂的相互作用跨越几个长度和时间尺度。第二，由于泡沫是一种易碎的不透明的相混合物，因此几乎不存在适当的测量技术。第一种流动实验是用光学方法观察泡沫在表面附近的运动。他们产生有趣的见解泡沫动力学和牛顿流体表现出相当大的偏差。然而，目前还没有具有合理的空间和时间分辨率的三维调查。同时，数值研究尚未完全建立，缺乏验证实验，在项目的第一阶段，将开发和验证泡沫流的新测量技术。在德累斯顿，研究液态金属流动的创新技术已经开发出来，其中一些是世界上独一无二的。这些技术将适用于泡沫和泡沫。特别是，电阻抗断层扫描，专利的Wire-Mesh传感器，X射线和中子射线照相术，独特的超快X射线断层扫描和用X射线跟踪3D打印示踪剂。初步研究已经表明，这些技术中有许多适用于泡沫。在项目的第二阶段，将应用测量技术系统地研究三种常见的泡沫流动：圆柱体周围的流动和后向台阶上的流动以及自由射流。通过与牛顿流体的比较，将确定和描述由粘弹性、屈服极限以及泡沫的液体分布、流变学和流体动力学之间的复杂相互作用引起的独特效应。开展大尺度实验的目的是首次观察和分析泡沫流的湍流结构，通过该项目的完成，将泡沫流动力学作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.