基于OpenFOAM的过冷流动沸腾数值模拟

过冷流动沸腾现象被广泛应用于工业生产和动力系统中,对该现象的准确预测是两相流CFD模拟的重要研究方向。本文详细阐述了该模拟过程中的欧拉两流体模型及相关辅助模型,基于开源CFD平台OpenFOAM,模拟了4.5 MPa下竖直圆管内的过冷流动沸腾,得到了截面空泡份额、液相平均温度及壁面温度沿轴向的分布。计算结果与实验值符合良好,说明了模型的有效性和程序的正确性。本文可为在OpenFOAM中添加新的模型及开发新的求解器以模拟过冷流动沸腾问题提供参考。     

CFD过冷沸腾模型及在燃料组件热通道模拟中的应用

论述了强迫对流流动中过冷沸腾先进的CFD模拟，重点研究了连续液体与气泡间的动量交换。在本研究中，CFX-5程序中基于两流体方法的壁面沸腾模型将与最新发展的无拖曳力模型关系式一起运用。本文主要描述了相间质量、热量、动量交换模型的概念。利用公开发表的管内流动实验结果来进行模型验证。 用壁面沸腾模型对燃料棒束中一个热通道内的过冷沸腾进行了模拟。模拟中考虑了为提高燃料组件热量传输性能而在格架中设置搅混叶片的影响。模拟结果显示了模型在评估格架几何设计对流动特性影响方面的能力。     

蒸汽发生器传热管束过冷沸腾区两相流动数值模拟

基于两流体欧拉数学模型结合RPI壁面沸腾模型,利用大型商用CFD软件ANSYS CFX 12.0对蒸汽发生器传热管束过冷沸腾区一次侧、壁面和二次侧耦合传热过程进行了数值模拟。研究了三叶梅花孔支撑板和不同入口过冷度条件下蒸汽发生器传热管束内的流动沸腾现象,得到一、二次侧流场与温度场,二次侧空泡份额分布,支撑板梅花孔局部的流动状况及不同入口过冷度对蒸汽发生器热工水力特性的影响。数值模拟结果表明,三叶梅花孔支撑板的存在及不同入口过冷度对蒸汽发生器传热管束过冷沸腾区域的热工水力特性影响显著。     

基于流固共轭传热的两相流动数值模拟及燃料子通道CHF预测研究

为对过冷沸腾两相流动进行准确模拟，并探索临界热流密度（CHF）预测方法，本文基于共轭传热和两相CFD分析的方法，通过流固界面耦合，建立流固共轭传热两相流动耦合求解的数值模型。首先通过典型燃料棒栅元过冷沸腾两相流动的模拟，验证数值模型的正确性。随后对燃料子通道内两相流动进行模拟，并在两相流动模拟的基础上，通过准瞬态的方法，建立与CHF试验过程非常近似的CHF预测方法，将加热壁面的温度飞升作为CHF判定的标准，实现对燃料组件子通道CHF的数值预测。研究表明，本文建立的数值模拟方法，可为燃料组件或其他换热系统的CHF预测奠定基础，为燃料组件的设计提供新的辅助手段。     

过冷沸腾自然对流两相CFD模拟及应用

采用计算流体力学（CFD）方法，开展过冷沸腾自然对流两相模拟与应用研究。对侧壁加热圆柱水箱过冷沸腾自然对流实验采用两相CFD瞬态模拟，模拟时间为1 500 s，通过模型设置与模拟方法研究，再现了过冷沸腾发生后实验的温度阶跃，得到与实验较一致的温度分布、气泡产生时间与产生位置，确保了数值计算的合理性与准确性。在此基础上，对以欧洲ESBWR（经济简化沸水堆）非能动安全壳冷却系统（PCCS）为原型的ISP-42实验进行了两相CFD模拟，获得与实验一致的温度分布，确定采用两相CFD数值模拟对非能动安全壳冷却系统及非能动余热排出系统进行应用研究可行，为下一步计算传热系数、构建自然对流传热模型建立了良好基础。该项研究对工程应用中探寻非能动安全壳冷却系统及非能动余热排出系统的两相自然循环传热特性具有较大价值。     

管内过冷流动沸腾CFD模型参数敏感性研究

采用CFD方法对燃料组件进行过冷流动沸腾数值模拟研究是反应堆热工水力分析的一项重要内容。本研究使用STAR CCM+基于欧拉双流体模型结合壁面沸腾模型对管内过冷流动沸腾进行数值模拟,得到了壁面温度、主流温度及空泡份额的分布。基于实验结果对网格模型、湍流模型、壁面沸腾模型及相间作用力模型的参数设置进行了敏感性分析。研究结果表明,对于欧拉双流体模型,并非网格量越多结果越准确,加热面第1层网格的高度对结果影响显著。湍流模型和曳力模型对计算结果影响较小,非曳力中的湍流耗散力及升力对结果影响较大。Li Quan或Hibiki Ishii汽化核心密度模型与Kocamustafaogullari气泡脱离直径模型组合对壁面温度及空泡份额的计算较准确。本研究可为反应堆燃料组件内过冷流动沸腾数值模拟提供参考依据。     

基于流固共轭传热的两相流动数值模拟及燃料子通道CHF预测研究

为对过冷沸腾两相流动进行准确模拟,并探索临界热流密度(CHF)预测方法,本文基于共轭传热和两相CFD分析的方法,通过流固界面耦合,建立流固共轭传热两相流动耦合求解的数值模型。首先通过典型燃料棒栅元过冷沸腾两相流动的模拟,验证数值模型的正确性。随后对燃料子通道内两相流动进行模拟,并在两相流动模拟的基础上,通过准瞬态的方法,建立与CHF试验过程非常近似的CHF预测方法,将加热壁面的温度飞升作为CHF判定的标准,实现对燃料组件子通道CHF的数值预测。研究表明,本文建立的数值模拟方法,可为燃料组件或其他换热系统的CHF预测奠定基础,为燃料组件的设计提供新的辅助手段。     

竖直窄缝水工质常压过冷沸腾流动与传热分析

以去离子水为工质,对常压下竖直窄缝通道内过冷沸腾流动与换热规律进行实验和数值模拟研究。对壁面气泡核化特点进行可视化实验分析,建立2 mm窄缝通道的壁面核化沸腾模型,包括:汽化核心密度、气泡脱离直径和气泡脱离频率关联式。以两流体模型为基础,结合壁面热量分配伦斯勒理工学院(RPI)模型以及壁面核化沸腾模型,建立竖直窄缝通道内过冷沸腾流动传热计算流体动力学(CFD)数值模型,对典型实验工况进行模拟分析,并与实验结果进行对比,两者吻合良好。     

过冷沸腾自然对流两相CFD模拟及应用

采用计算流体力学(CFD)方法,开展过冷沸腾自然对流两相模拟与应用研究。对侧壁加热圆柱水箱过冷沸腾自然对流实验采用两相CFD瞬态模拟,模拟时间为1 500 s,通过模型设置与模拟方法研究,再现了过冷沸腾发生后实验的温度阶跃,得到与实验较一致的温度分布、气泡产生时间与产生位置,确保了数值计算的合理性与准确性。在此基础上,对以欧洲ESBWR(经济简化沸水堆)非能动安全壳冷却系统(PCCS)为原型的ISP-42实验进行了两相CFD模拟,获得与实验一致的温度分布,确定采用两相CFD数值模拟对非能动安全壳冷却系统及非能动余热排出系统进行应用研究可行,为下一步计算传热系数、构建自然对流传热模型建立了良好基础。该项研究对工程应用中探寻非能动安全壳冷却系统及非能动余热排出系统的两相自然循环传热特性具有较大价值。     

基于OpenFOAM的5×5棒束流动数值模拟

为验证OpenFOAM燃料组件子通道单相棒束流动的有效性,利用在OpenFOAM中实现的SST k-ω模型对MATIS-H基准题进行了模拟。基于OpenFOAM求解子通道速度场和压力场。将OpenFOAM的模拟数据与MATIS-H基准试验的数据进行了对比。结果表明,在网格划分精度为3级时,OpenFOAM模拟CFD子通道单相流动数据与MATIS-H基准题数据吻合度较好。由于格架和搅混翼的存在,冷却剂向中心流道靠拢,高低压区分布明显,趋于中心对称。子通道内产生涡旋,加强了燃料棒表面换热。OpenFOAM在子通道CFD模拟上具有应用前景。     

基于气泡动力学的过冷流动沸腾边界层模型研究

过冷流动沸腾中的流动和传热特性对反应堆的安全运行和经济性都具有重要意义。过冷流动沸腾起始于ONB点,结束于Tsat点,中间被OSV点划分为高过冷流动沸腾段和低过冷流动沸腾段,不同阶段流场情况以及气泡行为存在较大区别。目前关于过冷流动沸腾过程的研究主要基于宏观实验、理论研究和数值模拟,随着气泡动力学的发展,从微观层面揭示沸腾机理变得可行。本文基于气泡动力学和气泡边界层模型,提出了一套预测过冷流动沸腾的理论模型,采用分相模型,将流场在径向上划分为多个区域,通过1组准二维控制方程,将各区域内的气泡行为,区域间的质量、动量和能量交换以及两相参数沿轴向的变化情况考虑在内,利用获得的边界层流场信息,可确定ONB点和OSV点。模型与空泡份额和流体温度的实验结果符合良好,并成功应用于核反应堆燃料元件通道的过冷流动沸腾计算。     

过冷流动沸腾中汽泡脱离直径的理论研究

汽泡脱离直径模型是壁面沸腾计算中的一个重要子模型。为了正确预测过冷流动沸腾中的壁面传热情况,研究结合新改进的汽泡生长模型,采用力平衡方法对过冷流动沸腾中的汽泡脱离直径进行了模拟。汽泡生长模型同时考虑了微液层、过热层和汽泡顶部过冷液体层对汽泡生长所做的贡献,并采用饱和沸腾与过冷沸腾2个实验对其进行了验证,结果表明预测曲线与实验值吻合良好。另外,选取了3个过冷流动沸腾实验来验证汽泡脱离直径模型,模拟结果均在可接受的误差范围内。      

Wall function approach for boiling two-phase flows

One of the important goals of the NURESIM project is to assess and improve the simulation capability of the three-dimensional two-fluid codes for prediction of local boiling flow processes. The boiling flow is strongly affected by local mechanisms in the turbulent boundary layer near the heated wall. Wall-to-fluid transfer models for boiling flow with the emphasis on near-wall treatment are being addressed in the paper. Since the computational grid of the 3D two-fluid models is too coarse to resolve the variable gradients in the near-wall region, the use of wall functions is a common approach to model the liquid velocity and temperature profile adjacent to the heated wall.The wall function model for momentum, based on the surface roughness analogy has been discussed and implemented in the NEPTUNE_CFD code. The model has been validated on several upward boiling flow experiments, differing in the geometry, working fluid and operating conditions. The simulations with the new wall function model show an improved prediction of flow parameters over the boiling boundary layer. Furthermore, a wall function model for the energy equation, based on enhanced two-phase wall friction has been derived and validated.     

Simulations of air–water flow and subcooled boiling flow using the CUPID code

This paper summarizes the physical models and a modified numerical procedure for the lift force of the CUPID code to simulate a subcooled boiling flow. A part of these physical models and the numerical procedure were verified through a calculation of air–water flow tests. A subcooled boiling flow was then calculated to assess the whole implementation. These assessments indicate that the implementation of the physical models and a modified numerical scheme are appropriate, and that the calculated primary variables of a subcooled boiling flow such as the liquid velocity and void fraction profiles can be acceptable in general, though IATE and a turbulence model for a two-phase flow are needed to be improved for a better prediction.     

矩形窄通道内汽泡滑移与冷凝前期生长模型研究

矩形窄流道内汽泡生长会直接改变相界面浓度，从而影响流道的传热传质性能。为获得适用于窄流道内不同类型的汽泡生长模型，基于通体可视的实验本体，开展壁面沸腾流动换热实验。基于传热能量方程，研究过冷沸腾中汽泡滑移与冷凝前期两种情况下汽泡生长模型。实验结果表明汽泡呈现两种形式的生长，即汽泡滑移生长以及冷凝前期生长。建立了两种情况下的汽泡生长模型，实验数据验证模型误差在20%以内。因此，本研究能为沸腾两相数值模拟提供更加精细化的汽泡生长模型，从而提高汽泡行为的预测精度。     

Numerical Simulation of Subcooled Boiling Inside High-Heat-Flux Component with Swirl Tube in Neutral Beam Injection System

In order to realize steady-state operation of the neutral beam injection（NBI） system with high beam energy,an accurate thermal analysis and a prediction about working conditions of heat-removal structures inside high-heat-flux（HHF） components in the system are key issues.In this paper,taking the HHF ion dump with swirl tubes in NBI system as an example,an accurate thermal dynamic simulation method based on computational fluid dynamics（CFD） and the finite volume method is presented to predict performance of the HHF component.In this simulation method,the Eulerian multiphase method together with some empirical corrections about the inter-phase transfer model and the wall heat flux partitioning model are considered to describe the subcooled boiling.The reliability of the proposed method is validated by an experimental example with subcooled boiling inside swirl tube.The proposed method provides an important tool for the refined thermal and flow dynamic analysis of HHF components,and can be extended to study the thermal design of other complex HHF engineering structures in a straightforward way.The simulation results also verify that the swirl tube is a promising heat removing structure for the HHF components of the NBI system.     

Numerical Simulation on Subcooled Boiling Heat Transfer Characteristics of Water-Cooled W/Cu Divertors

In order to realize safe and stable operation of a water-cooled W/Cu divertor under high heating condition,the exact knowledge of its subcooled boiling heat transfer characteristics under different design parameters is crucial.In this paper,subcooled boiling heat transfer in a water-cooled W/Cu divertor was numerically investigated based on computational fluid dynamic(CFD).The boiling heat transfer was simulated based on the Euler homogeneous phase model,and local differences of liquid physical properties were considered under one-sided high heating conditions.The calculated wall temperature was in good agreement with experimental results,with the maximum error of 5%only.On this basis,the void fraction distribution,flow field and heat transfer coefficient(HTC)distribution were obtained.The effects of heat flux,inlet velocity and inlet temperature on temperature distribution and pressure drop of a water-cooled W/Cu divertor were also investigated.These results provide a valuable reference for the thermal-hydraulic design of a water-cooled W/Cu divertor.     

Uncertainty Analysis on Boundary Condition in Subcooled Boiling Flow by Deterministic Sampling

In this work, the DEBORA subcooled boiling flow experiments were employed as benchmark and simulated by Fluent. The uncertainty from boundary conditions and its influence trend of the prediction of subcooled boiling flow were analyzed by using deterministic sampling method. The distributions of radial parameters were calculated and the confidence intervals were obtained. Besides, the uncertainty source contributions on radial parameters were also analyzed. The results show that the uncertainties of the inlet temperature and the wall heat flux play predominant roles on the prediction of radial void fraction, while the uncertainties of the operating pressure and the inlet temperature dominate calculation of radial liquid temperature.