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，我们还是经常对它们不同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：“泡沫塑料杯雕塑”），建筑师（贝京斯“水立方”）和研究人员（约翰阿奇博尔德惠勒：“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”。添加到泡沫上部区域的少量液体将均匀地向下渗透通过泡沫。然而，添加更大量的液体将导致泡沫的流动。与瑞利-泰勒不稳定性类似，具有大液体含量的泡沫向下移动，而具有小液体含量的泡沫向上移动。这种对流卷的出现在15年前就有记载。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。只有发病时的液体量有记录。在此基础上，一些部分矛盾的理论已经出版，解释了对流不稳定的发病。在这个项目中，对流不稳定将被系统地研究。为此，将采用数值模拟和实验相结合的方法。在实验中，对流不稳定性将被测量在具有不同横截面和宽范围的参数的垂直通道中。根据计算结果，可以得到一个状态图，这有助于在实际应用中预测不稳定性的出现。这些实验将与再现对流不稳定的相位平均数值模拟相结合。为此，将通过在真实泡沫中发生的效果来扩展流解算器。要做到这一点，必须对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。由此产生的流动求解器是解释对流不稳定的主要工具。定量分析了重要效应对失稳的影响，从而揭示了失稳的机理。最后，通过复杂的几何形状的液体泡沫的流动进行了研究，以获得一个测试的情况下，未来的泡沫流动调查的泡沫社区。

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.