Abstract The operating conditions of nuclear reactor vessels do not allow an easy access to thermal-hydraulics parameters. Thus, only macroscopic parameters can give information on the thermal hydraulic state of the vessel. Developments and validations of Computational Fluid Dynamics (CFD) tools become crucial to have a local view of the flow corresponding to the measured macroscopic parameters. In order to ensure accurate simulations of such flows, a well-known step-by-step procedure has been applied to a fluid thermal mixing case. A first step, called the Phenomena Identification and Ranking Table (PIRT) approach, consists of identifying all the potential physical phenomena that contribute to the target flow. These phenomena are then ordered according to two main criteria: their contribution level and their degree of maturity in terms of modelling. Based on this step, verification test cases are identified for each selected physical phenomenon. They are simulated with the Computational Fluid Dynamics (CFD) tool ANSYS Fluent. Mesh convergence are systematically done on these test cases. A specific effort is made on phenomena that have been considered with a high contribution and a low maturity level in the PIRT step. Then, the objective of the Validation step is the improvement of the modelling and meshing choices by considering single and multiple phenomena effects in the same flow. For this step, experimental studies are conducted by researchers from the University of Poitiers* (France). An experimental facility has been designed with an increasing level of flow complexity. Hydraulic and concentrations of passive tracer measurements are planned. Finally, uncertainty quantifications methods are explored to quantify the discretization errors and the sensibility of the simulations on some parameters (geometry, boundary conditions, etc.). This paper gives an overview of the step-by-step methodology applied to a specific fluid thermal mixing problem with illustrated examples at each step.

中文翻译：

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与流体热混合的不确定性量化方法相关的 PIRT 和 V&V

摘要 核反应堆容器的运行条件不允许轻松获得热工水力参数。因此，只有宏观参数才能提供有关船舶热工水力状态的信息。计算流体动力学 (CFD) 工具的开发和验证对于获得与测量的宏观参数相对应的流动的局部视图至关重要。为了确保对此类流动进行准确模拟，已将众所周知的分步程序应用于流体热混合案例。第一步，称为现象识别和排序表 (PIRT) 方法，包括识别对目标流有贡献的所有潜在物理现象。然后根据两个主要标准对这些现象进行排序：他们的贡献水平和他们在建模方面的成熟度。基于此步骤，为每个选定的物理现象识别验证测试用例。它们使用计算流体动力学 (CFD) 工具 ANSYS Fluent 进行模拟。网格收敛是在这些测试用例上系统地完成的。对在 PIRT 步骤中被认为具有高贡献和低成熟度级别的现象进行了特定的努力。然后，验证步骤的目标是通过考虑同一流中的单个和多个现象影响来改进建模和网格划分选择。对于这一步，普瓦捷大学*（法国）的研究人员进行了实验研究。一个实验设施的设计具有越来越高的流动复杂性。计划进行被动示踪剂测量的水力和浓度。最后，探索了不确定性量化方法来量化离散化误差和模拟对某些参数（几何、边界条件等）的敏感性。本文概述了应用于特定流体热混合问题的分步方法，并在每个步骤中提供了示例。