The flow structure of a bubble-driven liquid-metal jet in a horizontal magnetic field
The flow structure of a bubble-driven liquid-metal jet in a horizontal magnetic field
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DOI：
10.1017/s0022112006004423
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发表时间：
2007-03
影响因子：
3.7
通讯作者：
C. Zhang;S. Eckert;G. Gerbeth
中科院分区：
文献类型：
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作者：
C. Zhang;S. Eckert;G. Gerbeth
已知静磁场适合于阻尼导电液体中的平均流动和湍流运动。本文提出了一项考虑水平磁场对液态金属气泡驱动流动影响的实验研究。该研究的重点是由气体喷射产生的中心射流驱动的液态金属柱内的液体循环。流体容器具有圆形横截面和电绝缘壁。采用低气体流速，导致分离的气泡羽流在圆柱体轴线周围的点内上升。这种轴对称结构暴露在水平磁场中。我们提供了描述速度场的空间和时间结构的详细实验数据。使用超声多普勒测速仪（UDV）分别测量垂直和径向速度分量，首次能够完整绘制气泡驱动液态金属流的液体速度分布图。与普通气泡羽流相比，磁场极大地改变了流场的全局和局部特性。在这里考虑的参数范围内，我们没有发现先前的流动抑制，但事实上，对流运动的重组。原来的轴对称流场相对于磁场线的方向变得各向异性。在与磁场平行的平面中，向上流动占主导地位，而在正交平面中则强制进行再循环运动。与通常的预期相反，施加中等磁场（100 < Ha < 400，1 ≲ N ≲ 10）会破坏整体流动的稳定性，并产生具有主导频率的瞬态振荡流动模式。
Static magnetic fields are known to be suitable for damping mean flow and turbulent motion in an electrically conducting liquid. In this paper, an experimental study is presented considering the influence of a horizontal magnetic field on a bubble-driven flow of a liquid metal. The investigation is focused on the liquid circulation inside a liquid metal column driven by a central jet produced by gas injection. The fluid vessel has a circular cross-section and electrically insulating walls. Low gas flow rates were applied, resulting in a plume of separated bubbles rising inside a spot around the cylinder axis. This axisymmetric configuration is exposed to a horizontal magnetic field. We present detailed experimental data describing the spatial as well as the temporal structure of the velocity field. Measurements of the vertical and the radial velocity component, respectively, were performed using the ultrasound Doppler velocimetry (UDV), allowing for the first time a complete mapping of the liquid velocity distribution for a bubble-driven liquid metal flow. The magnetic field considerably modified the global and local properties of the flow field compared to an ordinary bubble plume. In the parameter range considered here we did not find a prior flow suppression, but, in fact, a restructuring of the convective motion. The original axisymmetric flow field became anisotropic with respect to the direction of the magnetic field lines. An upwards flow dominated in a plane parallel to the magnetic field, whereas the recirculating motion was enforced in the orthogonal plane. Contrary to usual expectations, the application of a moderate magnetic field (100 < Ha < 400, 1 ≲ N ≲ 10) destabilizes the global flow and gives rise to transient, oscillating flow patterns with predominant frequencies.