This paper presents an enstrophy-resolved simulation of the phase inversion problem using the volume of fluid (VOF) method. This well-known benchmark for modeling multiphase flows features a buoyancy-driven unsteady motion of a light fluid into a heavy one followed by several large- and small-scale interfacial processes such as deformation, ligament formation, interface breakup, and coalescence. A fully resolved description of such flow is advantageous for a priori and a posteriori evaluations when developing new subgrid-scale closure models for large eddy simulation of two-phase flows. However, most of the previous attempts in performing the direct numerical simulation of this problem have been unsuccessful to reach grid-independent high-order flow statistics such as enstrophy. The key contribution of this paper lies in proposing a new converging configuration for this problem by reducing the Reynolds and Weber numbers. The new setup reaches grid convergence for all the flow characteristics on a \(512^3\) grid. Particularly, the enstrophy which has always revealed a grid-dependent behavior in all the previous studies converges for the proposed setup. Also, we analyze the temporal evolution of interfacial structures including the statistics of the total interfacial area during the process on different grid resolutions. First, no convergence on the interfacial area is observed and the possible reasons for lack of convergence are discussed. The potential remedies are investigated through a comprehensive parameter study. The findings highlight that (i) the enstrophy always converges for these moderate Re and We numbers, and (ii) the convergence of the total interfacial area is sensitive to the choice of initial and wall boundary conditions. Then, a new setup based on this sensitivity analysis is proposed that succeeded in full convergence for enstrophy and a partial convergence for the total interfacial area. The numerical simulations were carried out using the VOF solvers of OpenFOAM with a comparison between the algebraic and geometric schemes. Besides, the convergence of size distribution of dispersed structures is investigated. The present study provides insight into the possible directions toward a DNS of phase inversion problem with all the flow and interfacial structures resolved, which is essential for the future development of multiphase flow models.

本文介绍了使用流体体积（VOF）方法对相转化问题进行旋涡分离的模拟。这个众所周知的基准用于模拟多相流，其特征在于，由浮力驱动的轻流体不稳定地运动为重流体，然后经历了各种大，小规模的界面过程，例如变形，韧带形成，界面破裂和聚结。当开发用于两相流的大涡流仿真的新的子网格规模的封闭模型时，对这种流的完全解析的描述对于先验和后验评估是有利的。但是，执行此问题的直接数值模拟的大多数先前尝试都无法获得独立于网格的高阶流量统计数据，例如回旋。本文的主要贡献在于通过减少雷诺数和韦伯数来为该问题提出一种新的收敛配置。新的设置使网格上所有流特征的网格收敛。\（512 ^ 3 \）网格。特别是，在所有先前的研究中始终揭示出网格依赖性行为的涡旋收敛于所提出的装置。此外，我们分析了界面结构的时间演变，包括在不同网格分辨率下过程中的总界面面积的统计数据。首先，没有观察到界面区域的收敛，并讨论了缺乏收敛的可能原因。通过全面的参数研究来研究潜在的补救措施。这些发现突出表明：（i）对于这些中等的Re和We数，内旋总是收敛的；并且（ii）总界面面积的收敛对初始边界条件和壁边界条件的选择敏感。然后，提出了一种基于这种敏感性分析的新设置，该方法成功实现了对虹膜的完全收敛和对整个界面区域的局部收敛。使用OpenFOAM的VOF解算器进行了数值模拟，并比较了代数方案和几何方案。此外，还研究了分散结构的尺寸分布的收敛性。本研究为解决所有流和界面结构的相转化问题的DNS的可能方向提供了见识，这对于多相流模型的未来发展至关重要。研究了分散结构尺寸分布的收敛性。本研究为解决所有流和界面结构的相转化问题的DNS的可能方向提供了见识，这对于多相流模型的未来发展至关重要。研究了分散结构尺寸分布的收敛性。本研究为解决所有流和界面结构的相转化问题的DNS的可能方向提供了见识，这对于多相流模型的未来发展至关重要。