Abstract

Liquid metals offer unique properties and their use in a nuclear fusion reactor, both as confined flows and free-surface flow, is widely studied in the fusion community. The interaction between this conductive fluid and the tokamak magnetic fields leads to magnetohydrodynamic (MHD) phenomena that influence the flow features. To properly design components that employ liquid metals, it is necessary to accurately predict these features, and although the efforts have been made in development, a mature code specifically customized to simulate MHD flows is still unavailable. In this work, the general purpose computational fluid dynamics code ANSYS CFX 18.2 is validated for MHD free-surface thin-film flow with insulated walls up to $Ha=1000$ and for several values of the characteristic width/thickness ratio, comparing the results with the theoretical relation available in the literature. For all the cases considered, the maximum integral error is found to be below 10%. Successively, the validated code is used to investigate the MHD flow in a chute with a characteristic film ratio equal to 0.1 and for $Ha=300$. Uniform and nonuniform wall electrical conductivity cases are considered with the latter modeled by placing on the side walls and on the back wall localized regions with different conductivity. The electrical conductivity of the back wall is found to have a negligible effect on the global flow when the lateral wall is insulated, similarly to what is observed for the analogous bounded flow. Contrariwise, an electrically conductive lateral wall is found to enhance the free-surface jet and to modify the Hartmann layer structure.

摘要

液态金属具有独特的性能，它们在核聚变反应堆中的使用，无论是受限流还是自由表面流，在聚变界都得到了广泛的研究。该导电流体与托卡马克磁场之间的相互作用导致影响流体流动特性的磁流体动力学（MHD）现象。为了正确设计使用液态金属的组件，必须准确地预测这些特征，并且尽管已在开发中进行了努力，但仍无法使用专门为模拟MHD流程而定制的成熟代码。在这项工作中，通用计算流体动力学代码ANSYS CFX 18.2已针对MHD自由表面薄膜流动进行了验证，绝热壁达到$H\mathrm{一种}=1000$对于特征宽度/厚度比的几个值，将结果与文献中可用的理论关系进行比较。对于所有考虑的情况，发现最大积分误差均低于10％。此后，经过验证的代码将用于研究特征膜比率等于0.1的斜道中的MHD流量，并且$H\mathrm{一种}=300$。考虑均匀和不均匀的壁电导率情况，后者通过放置在侧壁和后壁上具有不同电导率的局部区域来建模。当侧壁被绝缘时，发现后壁的电导率对整体流动的影响可忽略不计，这与类似的边界流动所观察到的相似。相反，发现导电侧壁增强了自由表面射流并改变了Hartmann层结构。