In monodisperse droplet streams, the inter-droplet distances can change in a manner that brings pairs or triplets of droplets closer to one another, a process known as grouping. In the advanced stages of this process, droplet pairs can coalesce to form larger droplets. The grouping mechanisms in these droplet streams are not yet fully understood. Potentially, such a process can be controlled by an acoustic field. In the present study, CFD simulations of isopropanol droplet streams in air were performed in ANSYS Fluent using the Eulerian-Lagrangian approach to analyze this process and to provide insight into grouping mechanisms. User-defined functions (UDFs) were used to tailor the code to the problems addressed here. Three scenarios were investigated. For the case of a single stream of droplet pairs, the mechanism of drag coefficient differences between the leading and trailing droplets enabled reproduction of the results of longitudinal grouping experiments. For the case of two parallel streams, the lift force enabled reproduction of lateral grouping trends which were observed in experiments. Finally, for a single droplet stream in an acoustic standing wave, the experimentally observed sequence of single droplets and droplet pairs, induced by the acoustic wave, was reproduced computationally. It was found that the acoustic field significantly affects both grouping behavior and the droplet distribution in the computational domain, thereby either enhancing or delaying grouping tendencies. These results strongly indicate the potential that lies in employing an acoustic field to exercise control over how, where and if droplet grouping occurs.

中文翻译：

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利用声驻波对液滴分组及其势能控制的数值研究

在单分散液滴流中，液滴间的距离会发生变化，使成对或三滴液滴彼此更靠近，这一过程称为分组。在此过程的高级阶段，液滴对可以合并形成更大的液滴。这些液滴流中的分组机制尚未完全了解。潜在地，这样的过程可以由声场控制。在本研究中，使用欧拉-拉格朗日方法在 ANSYS Fluent 中对空气中的异丙醇液滴流进行 CFD 模拟，以分析该过程并深入了解分组机制。用户定义函数 (UDF) 用于针对此处解决的问题定制代码。研究了三种情况。对于单个液滴对流的情况，前导液滴和尾随液滴之间阻力系数差异的机制能够再现纵向分组实验的结果。对于两条平行流的情况，升力能够再现实验中观察到的横向分组趋势。最后，对于声驻波中的单个液滴流，通过计算再现了由声波引起的实验观察到的单个液滴和液滴对序列。结果发现，声场显着影响计算域中的分组行为和液滴分布，从而增强或延迟分组趋势。这些结果有力地表明了利用声场来控制液滴如何、在何处以及是否发生液滴分组的潜力。