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中文核心期刊

垂直磁场下金属液滴撞击液池数值模拟研究: 尾涡与射流

NUMERICAL SIMULATION STUDY OF METAL DROPLETS IMPACTING A LIQUID POOL IN A VERTICAL MAGNETIC FIELD: TAIL VORTICES AND JETS

  • 摘要: 本文采用数值模拟方法系统研究了外部垂直磁场作用下金属液滴撞击同种液体液池的动力学行为. 基于轴对称坐标系, 结合改进的流体体积法(VOF)与自适应网格细化技术, 有效提升了界面追踪的精度与计算效率. 洛伦兹力被简化为外部体积力. 研究涵盖了雷诺数700至13000及韦伯数40至520的广泛参数区间. 通过对撞击过程中涡结构的演化分析, 将撞击现象划分为无涡脱、主涡脱和卡门涡街三种典型模式, 并据此构建了涡结构与射流形态的相图. 结果表明, 磁场强度和表面张力的增加均对溅射行为具有显著抑制作用, 且二者均可诱发从无涡脱向主涡脱的转变. 然而, 在高雷诺数区域, 表面张力对射流的抑制作用更为显著, 而对涡环结构影响有限; 垂直磁场则不仅影响涡环的形成与演化, 还能有效减缓射流的径向扩展速度. 进一步研究发现, 在连续涡脱并形成卡门涡街的情形下, 首次形成的射流在颈部区域呈现周期性摆动, 其摆动频率与卡门涡街的脱涡频率密切相关, 垂直磁场对射流初始摆动表现出非单调调控效应.

     

    Abstract: In this paper, the complex physical phenomenon of metal droplets impacting a pool of the same liquid under the action of an external vertical magnetic field is investigated in depth by means of numerical simulations. The study is carried out in an axisymmetric coordinate system, and in order to solve the Navier-Stokes (N-S) equations with the Lorentz force term accurately, the modified volume of fluid (VOF) method and adaptive mesh refinement technique are employed to treat the Lorentz force as an external volume force, which effectively improves the accuracy and computational efficiency of the numerical simulation. Under different Reynolds numbers (ranging from 700 to 13000) and Weber numbers (ranging from 40 to 520), the droplet impact phenomenon is carefully categorized into three types based on the evolution of vortex states: no vortex detachment, vortex detachment, and formation of von Karmen vortex street. The results show that in the case of no vortex shedding, the sputtering phenomenon can be significantly suppressed by increasing the magnetic field strength or the surface tension. In the case of vortex shedding and Von Karmen vortex street formation, the surface tension mainly inhibits the sputtering process, while the vertical magnetic field affects the structure of the vortex ring, resulting in a change in the morphology and distribution of the vortex ring, and slows down the outward motion of the sputtering jet, which changes the dynamics of the droplet field after impact. In particular, when a continuous vortex shedding process triggers the formation of a von Karmen vortex street, the first generated jet oscillates in its root region, and the frequency of the oscillation is closely related to the vortex shedding phenomenon of the von Karmen vortex street. Further analysis reveals that the vertical magnetic field has a non-monotonic influence on the initial oscillating behavior of the jet, which provides a key theoretical basis for a deeper understanding of the complex flow mechanisms during droplet impact in a magnetohydrodynamic environment.

     

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