Towards Fluid Dynamics of Foam and Froth

• Applicant: Dr.-Ing. Sascha Heitkam
• Subject Area: Fluid Mechanics ; Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 431077191

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.

• DFG Programme: Independent Junior Research Groups
• International Connection: Switzerland
• Cooperation Partner: Professor Dr. Pavel Trtik