Abstract Multiple spatial scale is an important characteristic of two phase flow phenomena. The micro-scale and macro-scale flow structures are obviously different in flow state and have different effects on the mass, momentum and energy transfer between two phases. Different modeling approaches have been developed for each scale physical phenomenon in traditional numerical simulations. However, it is difficult to simulate two phase flow systems with multi-scale flow structures simultaneously. In order to address this problem, a multi-scale two phase method is developed based on the combination of Volume of Fluid (VOF) interface capture method and Euler–Lagrange particle tracking method. The fundamental assumption of the present method is that there is a clear scale separation between VOF interfaces and bubbles. Therefore, VOF method with artificial compressive algorithm is used to simulate the dynamic evolution of macro-scale air-water interface. While Euler–Lagrange method is used to track the micro-scale bubbles that cannot be captured in grids. Collision, coalescence and breakup of Lagrange bubbles and two-way coupling are fully considered to construct a comprehensive micro-bubble solving procedure. Transformation criteria and the corresponding algorithms between micro-scale and macro-scale flow structures are designed and discussed in detail. In addition, a new curvature-based algorithm for the transformation from VOF interface to Lagrange bubbles is proposed. Simulations of typical two phase flow problems involving multi-scale flow transformation are carried out to test the performance of the multi-scale solver. Results indicate that the multi-scale two phase method performs significantly better than the pure VOF method in capturing micro-scale phenomena. Besides, the curvature-based transformation algorithm proposed in this paper is proved to be more precise and efficient than the previous identify-based one. From the perspective of simulation accuracy and efficiency, the multi-scale two phase method is more promising for the simulation of actual complex two-phase flows.

中文翻译：

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一种改进的气泡流多尺度两相法

摘要 多空间尺度是两相流现象的重要特征。微观尺度和宏观尺度的流动结构在流动状态上明显不同，对两相之间的质量、动量和能量传递有不同的影响。在传统的数值模拟中，已经为每个尺度的物理现象开发了不同的建模方法。然而，很难同时模拟具有多尺度流动结构的两相流系统。为了解决这个问题，基于流体体积（VOF）界面捕获方法和欧拉-拉格朗日粒子跟踪方法相结合，开发了一种多尺度两相方法。本方法的基本假设是 VOF 界面和气泡之间存在明显的尺度分离。所以，采用人工压缩算法的VOF方法模拟宏观尺度气水界面的动态演化。而欧拉-拉格朗日方法则用于跟踪网格中无法捕获的微尺度气泡。充分考虑了拉格朗日气泡的碰撞、聚结和破裂以及双向耦合，构建了一个综合的微气泡求解过程。详细设计和讨论了微观尺度和宏观尺度流动结构之间的转换标准和相应算法。此外，提出了一种新的基于曲率的 VOF 界面向拉格朗日气泡转换算法。对涉及多尺度流动变换的典型两相流问题进行了仿真，以测试多尺度求解器的性能。结果表明，多尺度两相方法在捕捉微尺度现象方面的性能明显优于纯 VOF 方法。此外，本文提出的基于曲率的变换算法被证明比以前的基于识别的变换算法更精确和有效。从模拟精度和效率的角度来看，多尺度两相法对于实际复杂两相流的模拟更有前景。