Abstract As the computational power of high-performance computing (HPC) facilities grows, so too does the feasibility of using first principle based simulation to study turbulent two-phase flows within complex pressurized water reactor (PWR) geometries. Direct numerical simulation (DNS), integrated with an interface capturing method, allows for the collection of high-fidelity numerical data using advanced analysis techniques. The presented research employs the massively parallel, finite-element based, unstructured mesh code, PHASTA, to simulate a set of two-phase bubbly flows through PWR subchannel geometries including auxiliary structures (spacer grids and mixing vanes). The main objective of the presented work is to analyze bubble dynamics and turbulence interactions at varying bubble concentrations to support the development of advanced two-phase flow closure models. Turbulent two-phase flows in PWR subchannels were simulated at hydraulic Reynolds numbers of 81,000 with bubble concentrations of 3%–15% by gas volume fraction (768–3928 resolved bubbles, respectively) and compared against a 1% void fraction case (262 bubbles) that had been previously simulated. The finite element mesh utilized for the study at higher bubble concentrations was composed of 1.55 billion elements, compared to the previous study which employed 1.11 billion elements, ensuring all turbulence scales and individual bubbles within the flow are fully resolved. For each case, the resolved initial bubble size was 0.65 mm in diameter (resolved with 25 grid points across the diameter). The simulations were analyzed to find flow features such as the mean velocity profile, bubble relative velocity and the effect of the bubbles on the turbulent conditions.

中文翻译：

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压水堆子通道中气泡数量效应的界面捕获模拟

摘要 随着高性能计算 (HPC) 设施计算能力的增长，使用基于第一性原理的模拟来研究复杂压水反应堆 (PWR) 几何结构内的湍流两相流的可行性也在增加。直接数值模拟 (DNS) 与界面捕获方法相结合，允许使用高级分析技术收集高保真数值数据。所提出的研究采用大规模并行、基于有限元的非结构化网格代码 PHASTA 来模拟一组通过 PWR 子通道几何结构的两相气泡流，包括辅助结构（间隔网格和混合叶片）。所提出工作的主要目标是分析不同气泡浓度下的气泡动力学和湍流相互作用，以支持先进的两相流闭合模型的开发。PWR 子通道中的湍流两相流以 81,000 的水力雷诺数进行模拟，气泡浓度按气体体积分数计为 3%–15%（分别为 768–3928 个解析气泡），并与 1% 空隙率情况（262 个气泡）进行比较) 之前已经模拟过。在较高气泡浓度下用于研究的有限元网格由 15.5 亿个元素组成，而之前的研究使用了 11.1 亿个元素，确保流动中的所有湍流尺度和单个气泡都得到完全解析。对于每种情况，解析的初始气泡大小为 0。直径为 65 毫米（通过直径上的 25 个网格点解析）。分析模拟以找出流动特征，例如平均速度剖面、气泡相对速度和气泡对湍流条件的影响。