Abstract The core of a Liquid Metal Fast Breeder Reactor (LMFBR) consists of cylindrical fuel rods that are wrapped by a helicoidally-wound wire spacer to enhance mixing and to prevent damage by fretting. It is known that the liquid metal close to the rod is forced to follow the wires, and that liquid metal further away from the rod crosses the wires (called: migratory flow). This work aims at gaining more insight into the physics behind migratory flow and to provide a model for its bending angle. To this purpose, the flow field in a 7-rods, wire-wrapped, hexagonal bundle with water is studied within the Reynolds number range of 4990–16330 by using Particle Image Velocimetry (PIV). Refraction of the light is minimized by using Fluorinated Ethylene Propylene (FEP), which is a refractive index-matching (RIM) material. These measurements confirm that liquid near the rod follows the helicoid path and bends cross-wise with respect to the wire further away from the rod. A theoretical model for the bending angle of the flow is derived from the Euler equations and shows that the bending is primarily caused by the pressure gradient field induced by the wire. The model shows a very good correspondence with the experimentally obtained PIV data. These findings improve our understanding of the physics at play in rod bundle flows with wrapped wires and can be of assistance in developing practical correlations for frictional pressure losses and heat transfer in such bundles.

中文翻译：

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了解杆束中螺旋线间隔器引起的迁移流：实验和理论研究

摘要 液态金属快速增殖反应堆 (LMFBR) 的核心由圆柱形燃料棒组成，燃料棒由螺旋缠绕的金属丝间隔件包裹，以增强混合并防止微动损坏。众所周知，靠近棒的液态金属被迫跟随金属丝，远离棒的液态金属穿过金属丝（称为：迁移流）。这项工作旨在更深入地了解迁移流背后的物理学，并为其弯曲角度提供模型。为此，使用粒子图像测速法 (PIV) 在 4990-16330 的雷诺数范围内研究了 7 杆、绕线、六边形带水束中的流场。通过使用氟化乙烯丙烯 (FEP)，它是一种折射率匹配 (RIM) 材料，可以最大限度地减少光的折射。这些测量证实杆附近的液体遵循螺旋路径并相对于远离杆的线横向弯曲。流动弯曲角的理论模型是从欧拉方程推导出来的，它表明弯曲主要是由导线引起的压力梯度场引起的。该模型与实验获得的 PIV 数据非常吻合。这些发现提高了我们对缠绕线棒束流中物理现象的理解，并有助于开发此类束中摩擦压力损失和热传递的实际相关性。流动弯曲角的理论模型是从欧拉方程推导出来的，它表明弯曲主要是由导线引起的压力梯度场引起的。该模型与实验获得的 PIV 数据非常吻合。这些发现提高了我们对缠绕线棒束流中物理现象的理解，并有助于开发此类束中摩擦压力损失和热传递的实际相关性。流动弯曲角的理论模型是从欧拉方程推导出来的，它表明弯曲主要是由导线引起的压力梯度场引起的。该模型与实验获得的 PIV 数据非常吻合。这些发现提高了我们对缠绕线棒束流中物理现象的理解，并有助于开发此类束中摩擦压力损失和热传递的实际相关性。