Transition between quasi-two-dimensional and three-dimensional Rayleigh-Benard convection in a horizontal magnetic field
Transition between quasi-two-dimensional and three-dimensional Rayleigh-Benard convection in a horizontal magnetic field
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水平磁场中准二维和三维瑞利-贝纳德对流之间的转变
DOI：
10.1103/physrevfluids.3.013503
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发表时间：
2018
影响因子：
2.7
通讯作者：
Sven Eckert
中科院分区：
文献类型：
--
作者：
Tobias Vogt;Wataru Ishimi;Takatoshi Yanagisawa;Yuji Tasaka;Ataru Sakuraba;Sven Eckert
采用实验和数值模拟相结合的方法，研究了矩形截面、纵横比为5的矩形箱中液态金属的磁流体动力学Rayleigh-Bénard对流。施加足够强的水平磁场将对流运动转换成平行于磁场布置的准二维（准2D）卷的流型。本文的目的是提供流场的详细描述，这通常被认为是准二维的。在本文中，我们专注于从准二维状态向三维流动发生的磁场强度下降的过渡。我们提出了系统的流量测量，通过超声多普勒测速。测量的数据提供洞察的主要对流辊的动力学，二次流引起的埃克曼泵，他们揭示了存在的小涡周围的对流辊的发展。新的流态已被确定的速度测量，这表明一个明显的表现为三维流动结构的比例增加。对流辊的一次旋转运动与二次流之间的相互作用变得越来越强。对流辊的显著膨胀导致由Ekman泵送驱动的原始再循环回路分解成几个较小的单元。流动测量是通过直接数值模拟完成的。数值模拟已被证明能够定性地再现实验中新发现的流态。
Magnetohydrodynamic Rayleigh-Bénard convection was studied experimentally and numerically using a liquid metal inside a box with a square horizontal cross section and an aspect ratio of 5. Applying a sufficiently strong horizontal magnetic field converts the convective motion into a flow pattern of quasi-two-dimensional (quasi-2D) rolls arranged parallel to the magnetic field. The aim of this paper is to provide a detailed description of the flow field, which is often considered as quasi-2D. In this paper, we focus on the transition from a quasi-two-dimensional state toward a three-dimensional flow occurring with decreasing magnetic-field strength. We present systematic flow measurements that were performed by means of ultrasound Doppler velocimetry. The measured data provide insight into the dynamics of the primary convection rolls, the secondary flow induced by Ekman pumping, and they reveal the existence of small vortices that develop around the convection rolls. New flow regimes have been identified by the velocity measurements, which show a pronounced manifestation of three-dimensional flow structures as the ratioincreases. The interaction between the primary swirling motion of the convection rolls and the secondary flow becomes increasingly strong. Significant bulging of the convection rolls causes a breakdown of the original recirculation loop driven by Ekman pumping into several smaller cells. The flow measurements are completed by direct numerical simulations. The numerical simulations have proven to be able to qualitatively reproduce the newly discovered flow regimes in the experiment.