Abstract Pressurized water reactors (PWRs) are the most common types of electricity generating nuclear reactors. Within their cores, fuel rods generate heat by fission and the high-pressure water is used as a coolant. The heated water is then used as a heat source in a steam generator that boils water in the secondary loop. The steam is used to spin a turbine and generate electricity. Spacer grids are key components of a PWR’s core. Their objectives are to maintain the fuel rods at their positions and enhance the coolant mixing and heat exchange. Over the past decades, numerous experimental and numerical studies have been performed, to characterize the flow induced by different types of spacer grids. The recent advancements of the computational description of the above-mentioned flows, led to a shift to higher resolution models for turbulence like Large Eddy Simulations. Therefore, highly spatially resolved experimental data is needed for code validation. The comparison and usage of the data about the flow in rod bundles with spacer grids obtained by different research groups is challenging. One major reason comes from the fact that the majority of the spacer grids studied are proprietary, and their geometries cannot be disclosed. The data required for some purposes like numerical code validation do not necessarily have to originate from one specific type of spacer grid. It is important to provide a detailed overview of the geometry tested and the experimental conditions. Equally crucial is to possess high spatial resolution and well-quantified and low relative uncertainty. In this study, a new, non-proprietary spacer grid is designed and 3D-printed. The flow induced by the spacer grid is characterized in a 5 × 5 rod bundle facility with Matching of Index of Refraction (MIR) at a Reynolds number Re = 27 , 390 using particle image velocimetry techniques. A complete uncertainty analysis is performed accounting for a variety of uncertainty sources. A low relative uncertainty is obtained. Eight middle-of-subchannel planes are selected as the domain of interest for this paper. Highly spatially resolved statistical results for the velocities, root-mean-square (RMS) fluctuating velocities, and Reynolds stresses are obtained along the span-wise direction of the flow, starting at the edge of the spacer grid up to 4.3 hydraulic diameters. The cross-flow between subchannels induced by the spacer grid is sustained for all the domain assessed. The turbulence induced by the spacer grid is assessed with the use of two-points cross-correlations and with the comparison of the RMS fluctuating velocities at different elevations. An increase of the size of the turbulent vortices along the span-wise direction is related to the decrease in the rms fluctuating velocities to evidence the turbulent dissipation. Differences between the size of the turbulent structures found with integral length scale calculations in the stream-wise and span-wise directions are attributed to the turbulence anisotropy. The full dataset and spacer grid geometry design will be available on the research group website of the authors. The data obtained can be used by other groups according to their interests.

中文翻译：

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具有 3-D 打印通道型间隔网格的棒束中湍流的实验测量

摘要 压水反应堆 (PWR) 是最常见的发电核反应堆类型。在它们的核心内，燃料棒通过裂变产生热量，高压水用作冷却剂。然后将加热的水用作蒸汽发生器中的热源，该蒸汽发生器将二次回路中的水煮沸。蒸汽用于旋转涡轮机并发电。隔栅是压水堆核心的关键组件。他们的目标是将燃料棒保持在其位置并增强冷却剂混合和热交换。在过去的几十年里，已经进行了大量的实验和数值研究，以表征由不同类型的间隔网格引起的流动。上述流程的计算描述的最新进展，导致转向更高分辨率的湍流模型，如大涡模拟。因此，代码验证需要高度空间解析的实验数据。不同研究小组获得的具有间隔网格的杆束中流动数据的比较和使用具有挑战性。一个主要原因来自这样一个事实，即所研究的大多数间隔网格都是专有的，它们的几何形状无法公开。某些目的（如数字代码验证）所需的数据不一定来自一种特定类型的间隔网格。提供所测试几何形状和实验条件的详细概述非常重要。同样重要的是拥有高空间分辨率、良好量化和低相对不确定性。在这项研究中，一个新的，非专有的间隔网格是设计和 3D 打印的。由间隔网格引起的流动在 5 × 5 棒束设施中使用粒子图像测速技术在雷诺数 Re = 27, 390 处进行折射率匹配 (MIR) 进行表征。对各种不确定性来源进行了完整的不确定性分析。获得了较低的相对不确定性。选择八个中间子通道平面作为本文的感兴趣域。速度、均方根 (RMS) 波动速度和雷诺应力的高度空间解析统计结果是沿着流动的展向方向获得的，从间隔网格的边缘开始，直到 4.3 水力直径。由间隔网格引起的子通道之间的交叉流对于所有评估的域都是持续的。由间隔网格引起的湍流是通过使用两点互相关和比较不同高度的 RMS 波动速度来评估的。沿展向方向的湍流涡旋尺寸的增加与 rms 波动速度的减小有关，以证明湍流耗散。在流向和展向方向上用积分长度尺度计算发现的湍流结构的大小之间的差异归因于湍流各向异性。完整的数据集和间隔网格几何设计将在作者的研究小组网站上提供。获得的数据可以由其他组根据他们的兴趣使用。