Investigation of the convective instability in liquid foam

液体泡沫存在于我们日常生活的许多方面（化妆品，食品）。尽管如此，我们仍然经常对它们不寻常的行为感到惊讶和惊讶。也许这就是为什么泡沫是艺术家（塔拉·多诺万的“泡沫塑料杯雕塑”）、建筑师（北京的“b水立方”）和研究人员（约翰·阿奇博尔德·惠勒的“量子泡沫”）的灵感来源。在过去的三十年里，我们在研究液体泡沫方面取得了很好的进展。尽管如此，许多复杂的影响还没有得到很好的理解。这种复杂效应的一个例子是“对流不稳定性”。少量的液体被加入到泡沫的上部区域，将均匀地向下渗透通过泡沫。然而，加入大量的液体会导致泡沫流动。类似于瑞利-泰勒不稳定性，含液量大的泡沫向下移动，含液量小的泡沫向上移动。这种对流卷的出现是在15年前被记录下来的。然而，其机制仍不清楚。事实上，它的形状和特征从未被系统地调查过。只有其发病的液体量已被记录。在此基础上，已经发表了几个部分相互矛盾的理论来解释对流不稳定性的开始。本项目将系统地研究对流不稳定性。为此，将采用数值模拟与实验相结合的方法。在实验中，对流不稳定性将在不同截面的垂直通道中测量，参数范围很广。从这些结果中，将得到一个状态图，这有助于在实际应用中预测不稳定性的出现。实验将与相位平均数值模拟相结合，再现对流不稳定性。为此，流动求解器将通过在真实泡沫中发生的效果来扩展。为此，有必要对其影响进行分析性描述。它们将从本项目范围内的文献、自己的初步工作和相位解析模拟中提取。由此得到的流动求解器是解释对流不稳定性的主要工具。重要的影响因素对不稳定性的影响将被量化，从而深入了解其机理。最后，对泡沫流体在复杂几何结构中的流动进行了数值和实验研究，为今后泡沫界的泡沫流动研究提供了一个试验案例。

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.