[论文解读] Implementation and validation of two-phase boiling flow models in OpenFOAM

Kai Fu, Henryk Anglart|arXiv (Cornell University)|Sep 6, 2017

Lattice Boltzmann Simulation Studies被引用 3

一句话总结

本文在 OpenFOAM 中采用雷诺平均湍流模型的两流体方法，实现了两相沸腾流模型的构建与验证。该模型通过界面传热、相变及界面面积浓度的封闭关系式，成功预测了欠热和饱和核态沸腾，与实验数据在空隙率和温度分布方面具有良好的一致性，但因聚并建模的局限性，气泡尺寸预测性能仍不理想。

ABSTRACT

Prediction of two-phase boiling flows using the computational fluid dynamics (CFD) approach is very challenging since several sub-models for interfacial mass, momentum and energy transfer in such flows are still not well established and require further development and validation. Once validating a particular model, it is important that all key parameter involved in the model are carefully verified. Such verification is typically performed by separate effect tests, where one parameter at a time is compared to a measured or otherwise known value. Needless to say that for complex models, which are typical for CFD applications to two-phase flow, the number of independent parameters that need to be verified can be quite high. This particular feature makes the validation process of complex CFD models in open source codes very attractive, since full access to the implementation details is possible. This paper is concerned with implementation and validation of two-phase boiling bubbly flow models using the OpenFOAM, open source environment. The model employs the two-fluid formulation of the conservation equations with the Reynolds-averaged treatment of the turbulent terms. The model consists of six conservation equations for the liquid and the vapor phase, allowing for the thermodynamic non-equilibrium and compressibility of both phases. In addition, the model includes two transport equations for the turbulence kinetic energy and energy dissipation and one transport equation for the interfacial area concentration. New models for wall heat partitioning as well as for the phase change terms in nucleate boiling have been implemented. Sensitivity studies as well as validation of the model against measured data available in the open literature have been performed and it has been shown that a reasonable agreement between predictions and experiments has been achieved.

研究动机与目标

• 在开源 CFD 软件 OpenFOAM 中开发并实现一个全面的两相沸腾流模型，以实现对欠热和饱和核态沸腾的精确模拟。
• 解决两相沸腾流中界面质量、动量和能量传递缺乏验证的封闭关系式的问题。
• 通过开源方式公开实现细节，实现对复杂 CFD 模型的完整验证与验证。
• 提高在加热管道中垂直向上流动条件下，空隙率、温度分布及相变机制的预测精度。
• 识别当前界面面积输运模型的局限性，特别是对气泡尺寸分布的预测能力。

提出的方法

• 采用包含六个守恒方程的两流体公式，涵盖液相和汽相，考虑热力学非平衡态和可压缩性。
• 引入湍流动能、耗散率及界面面积浓度（IAC）的输运方程，以闭合系统。
• 实现了用于核态沸腾中壁面传热分配和相变项的新模型，包括淬火、显热加热和蒸汽生成。
• 采用 Boussinesq 假设进行湍流应力建模，并应用标准 k-ε 湍流模型及壁面函数。
• 对界面速度采用迎风格式离散化，并引入源/汇项以描述气泡聚并、破碎和成核过程。
• 通过敏感性分析和对湍流分散力系数等参数的参数调优，利用 Bartolomej 和 DEBORA 实验数据对模型进行验证。

实验结果

研究问题

• RQ1 能否在 OpenFOAM 中成功实现一个包含全面封闭关系式的两流体两相沸腾模型，用于欠热流沸腾模拟？
• RQ2 与实验数据相比，该模型在垂直向上流动中对空隙率和液相温度分布的预测精度如何？
• RQ3 关键模型参数（特别是湍流分散力系数）对预测精度的影响是什么？
• RQ4 为何预测的气泡尺寸在测试段显著被低估？这对当前界面面积输运模型意味着什么？
• RQ5 该模型在多大程度上能再现实验测得的径向温度分布及相变机制？

主要发现

• 该模型在 Bartolomej 和 DEBORA 两个测试案例中，对空隙率和液相温度分布的预测与实验数据具有合理的吻合度。
• 敏感性分析表明，湍流分散力系数在 1.0 至 2.5 的范围内显著提升了整体预测精度。
• 径向温度分布的预测与实测数据高度一致，表明热场解析能力可靠。
• 气泡尺寸预测表现不理想，观测区域中存在显著低估，可能源于对气泡聚并速率的低估。
• 该模型在 OpenFOAM 中的实现方式实现了完全透明与可验证，支持后续对沸腾流封闭关系式的进一步开发。
• 研究结果凸显了改进界面面积输运模型的必要性，特别是针对欠热沸腾中聚并与破碎过程的建模。