Comparative Investigation of Eulerian and VOF Models in Gas-Liquid Two-Phase Flow Simulation
Authors: Sun Zhiyuan , He Wen , Han Jinyu , Liu Zhanwei , Bo Hanliang 
Published: November 2024

Abstract
In the field of nuclear engineering thermal hydraulics, accurately simulating gas-liquid two-phase flow is crucial for assessing the safety and efficiency of nuclear reactors. This study comprehensively compares two main computational methods for simulating gas-liquid two-phase flow — the Eulerian model and the Volume of Fluid (VOF) model, and explores the progress in coupling research of these two models. This paper first elaborates on the theoretical basis, assumptions, and fundamental equations of each model. The Eulerian model, which treats each phase as an interpenetrating continuum, is widely recognized for its computational efficiency and effectiveness in processing mixed flows. Although its treatment of phase boundaries is somewhat general, it excels in capturing momentum transfer and complex interactions observed in multiphase flows, thus becoming an important tool for nuclear reactor safety analysis. In contrast, the VOF model demonstrates outstanding accuracy in tracking fluid interfaces, which is essential for detailed analysis of interactions. It is suitable for scenarios that require precise delineation of fluid interfaces, such as simulating free surface flows and droplet formations. Although the VOF model requires higher computational resources, it provides a detailed analysis of interface phenomena, thereby facilitating a deeper understanding of flow dynamics. Our review of previous researchers’ comparative studies clearly exhibits the individual strengths and application characteristics of both models. Additionally, by simulating a gas-liquid two-phase flow bubble column case, we explore the differences between these two models from a macro perspective. Each model has its advantages at different flow scales: the Eulerian model is suitable for handling large-scale dispersed flows with accurate and efficient computation; the VOF model is apt for separated flows, accurately displaying interface information. However, in actual industrial applications, two-phase flows often contain both dispersed and separated flows, with interfaces at different scales. To bridge this gap, developing complex coupled methods that combine Eulerian and VOF models has become a focal point of research. We analyze various coupled models that integrate key features of the foundational models, aiming to mitigate their individual limitations and enhance simulation accuracy and reliability. The paper mainly discusses the coupled models in commercial software ANSYS Fluent and open-source software OpenFOAM, as well as their research progress. Looking forward, the paper outlines potential research directions to advance the development of coupled model technology. In conclusion, the work presented not only emphasizes the strengths and limitations of individual multiphase flow models but also showcases the potential of coupled models. These models are expected to have a significant impact in the field, offering more reliable and effective solutions for engineering and scientific exploration. These conclusions contribute to the development of multiphase flow in the field of nuclear engineering thermal hydraulics.