Abstract Recent advancements in computing power allow utilization of state-of-the-art direct numerical simulations (DNSs), coupled with interface tracking techniques, to perform fully resolved simulations of complex two-phase flows, such as flow regime transitions. Studying the highly resolved temporal and spatial information produced from these virtual experiments can advance our understanding of the phenomenon and inform coarser models. With these improved models, better predictions of flow regime behavior and location in boiling water reactors can be made. The presented research uses the PHASTA code, which employs the level set method for interface tracking, to examine the mechanisms of flow regime transition, specifically the slug-to-bubbly and slug-to–churn-turbulent regime transitions. The DNS was validated using theoretical and experimental work found in open literature. Different geometries, including pipes and minichannels, were explored in order to improve the fundamental understanding of the complex flow phenomenon. Using advanced analysis techniques, the transient flow properties were analyzed at resolutions not available to other methods. The numerical data analysis allows for calculation of both time and spatially averaged properties as well as local instantaneous properties. Possible mechanisms for the transition are discussed. Examples include liquid kinetic energy/surface tension energy balance and interfacial shear forces in the liquid film. It is also noted that the transition out of slug flow can take at least two pathways: interfacial wave-induced instability development in the Taylor bubble, leading to its disintegration, or strong bubble shearing at the tail of the bubble.

中文翻译：

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使用高分辨率虚拟实验探索两相流态转换机制

摘要 计算能力的最新进展允许利用最先进的直接数值模拟 (DNS)，结合界面跟踪技术，对复杂的两相流（例如流态转换）进行完全解析的模拟。研究从这些虚拟实验中产生的高分辨率时间和空间信息可以促进我们对这一现象的理解并为更粗略的模型提供信息。通过这些改进的模型，可以更好地预测沸水反应堆中的流态行为和位置。所提出的研究使用 PHASTA 代码，它采用水平集方法进行界面跟踪，以检查流态转换的机制，特别是段塞到气泡和段塞到搅动湍流状态转换。使用公开文献中的理论和实验工作验证了 DNS。探索了不同的几何形状，包括管道和微型通道，以提高对复杂流动现象的基本理解。使用先进的分析技术，以其他方法无法获得的分辨率分析瞬态流动特性。数值数据分析允许计算时间和空间平均特性以及局部瞬时特性。讨论了过渡的可能机制。例子包括液体动能/表面张力能量平衡和液膜中的界面剪切力。还应注意的是，段塞流的过渡至少可以采取两种途径：泰勒气泡中界面波引起的不稳定性发展，