Convection patterns in a liquid metal under an imposed horizontal magnetic field
Convection patterns in a liquid metal under an imposed horizontal magnetic field
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施加水平磁场下液态金属中的对流模式
DOI：
10.1103/physreve.88.063020
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发表时间：
2013
影响因子：
2.4
通讯作者：
Y. Takeda
中科院分区：
文献类型：
--
作者：
Yanagisawa;T.;Y. Hamano;T. Miyagoshi;Y. Yamagishi;Y. Tasaka;Y. Takeda
我们进行了实验室实验的瑞利-贝纳德对流与液体镓在不同强度的均匀施加的水平磁场。超声波速度剖面法被用来可视化的时空结构的流动，同时监测的温度波动的液体镓层。探索瑞利数Ra范围从临界值开始对流; Ekrasekhar numbercovers值高达1100。对流模式的状态图，建立了与Ra和值的方形容器的长宽比为5。我们确定了五个流动状态：（I）波动的大规模模式，没有轧辊，（II）弱约束辊与波动，（III）辊的连续振荡，（IV）重复辊数过渡与随机反转的流动方向，和（V）稳定的二维（2D）辊。这些流动状态通过Ra/值（浮力与洛伦兹力的比率）分类。温度时间序列的功率谱表明，区域I和II具有发达湍流的特征，而其他区域则没有。稳定的2D卷（Busse气球）的区域延伸到高Ra值，在本设置中的水平磁场和制度V位于Busse气球内。关于二维稳态滚转的不稳定性，区域III是由振荡不稳定性发展而来的行波对流。制度IV可以被视为相湍流的状态，这是由间歇性发生的斜静脉曲张不稳定性。
We performed laboratory experiments of Rayleigh-Bénard convection with liquid gallium under various intensities of a uniform imposed horizontal magnetic field. An ultrasonic velocity profiling method was used to visualize the spatiotemporal structure of the flows with simultaneous monitoring of the temperature fluctuations in the liquid gallium layer. The explored Rayleigh numbers Ra range from the critical value for onset of convection to; the Chandrasekhar numbercovers values up to 1100. A regime diagram of the convection patterns was established in relation to the Ra andvalues for a square vessel with aspect ratio 5. We identified five flow regimes: (I) a fluctuating large-scale pattern without rolls, (II) weakly constrained rolls with fluctuations, (III) a continuous oscillation of rolls, (IV) repeated roll number transitions with random reversals of the flow direction, and (V) steady two-dimensional (2D) rolls. These flow regimes are classified by the Ra/values, the ratio of the buoyancy to the Lorentz force. Power spectra from the temperature time series indicate that regimes I and II have the features of developed turbulence, while the other regimes do not. The region of steady 2D rolls (Busse balloon) extends to high Ra values in the present setting by a horizontal magnetic field and regime V is located inside the Busse balloon. Concerning the instabilities of the steady 2D rolls, regime III is the traveling wave convection developed from the oscillatory instability. Regime IV can be regarded as a state of phase turbulence, which is induced by intermittent occurrences of the skewed-varicose instability.