Investigation of the convective instability in liquid foam

• Applicant: Dr.-Ing. Sascha Heitkam
• Subject Area: Fluid Mechanics ; Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 280187655

Liquid foam is present in many aspects of our daily life (Cosmetic, Food). Still, we are often surprised and amazed by their unusual behaviour. Maybe thats why foam is a source of inspiration for artists (Tara Donovan: 'Styrofoam Cup Sculpture'), architects (Bejings 'Water Cube') and researchers (John Archibald Wheeler: 'Quantum foam'). In the last three decades we made good progress in investigating liquid foam. Still, many complex effects are not yet well understood. One example for such a complex effect is the 'convective instability'. A small amount of liquid that is added to the upper region of foam will seep downward through the foam uniformly. However, adding a larger amount of liquid will cause flowing of the foam. Similar to a Rayleigh-Taylor instability foam with large liquid content moves downward and foam with a small liquid content moves upward. The appearance of this convective roll was documented more than 15 years ago. However, its mechanism is still not understood. In fact, its shape and features were never surveyed systematically. Only the amount of liquid for its onset has been documented. On this basis, several, partly contradicting theories have been published that explain the onset of the convective instability. In this project, the convective instability will be investigated systematically. To this end, a combination of numerical simulations and experiments will be applied. In the experiment, the convective instability will be measured in vertical channels with different cross-sections and in a wide range of parameters. From the results, a regime-map will be derived, that helps to predict the appearence of the instability in practical applications. The experiments will be combined with phase-averaging numerical simulations that reproduce the convective instability. For this purpose, a flow solver will be extended by effects that take place in realistic foam. To do so, analytical descriptions of the effects are necessary. They will be extracted from literatur, own preliminary work and phase-resolving simulations in the scope of this project. The resulting flow solver is the main tool for explaining the convective instability. The influence of important effects on the instability will be quantified and thus, its mechanism fathomed. Finally, the flow of liquid foam through complex geometries is investigated numerically and experimentally in order to derive a test case for future foam flow investigations in the foam community.

• DFG Programme: Research Grants
• International Connection: France
• Cooperation Partners: Professorin Dr. Wiebke Drenckhan, Ph.D.; Professor Dr. Reinhard Höhler