Transition to magnetorotational turbulence in Taylor-Couette flow with imposed azimuthal magnetic field
Transition to magnetorotational turbulence in Taylor-Couette flow with imposed azimuthal magnetic field
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DOI：
10.1088/1367-2630/17/9/093018
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发表时间：
2015-09-11
影响因子：
3.3
通讯作者：
Avila, M.
中科院分区：
文献类型：
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作者：
Guseva, A.;Willis, A. P.;Avila, M.
磁旋不稳定性（MRI）被认为是天体物理吸积盘中湍流和动量输运的一个强大来源，但获得其运行的观测证据是具有挑战性的。最近，在室外施加轴向和方位磁场的Taylor-Couette流的实验室实验中，MRI显示了接近不稳定开始的运动学和动力学特性。虽然与线性稳定性分析很好地一致，但对MRI向湍流和输运性质的转变知之甚少。我们在这里报告了一个数值研究的MRI与强加的方位磁场。我们证明了层流Taylor-Couette流通过一个超临界Hopf分岔变成一个在方位方向上旋转而在轴向上停留的不稳定波。随后，流的特征是由亚临界次谐波Hopf分岔介导的灾难性过渡到时空缺陷。我们的结果与PROMISE实验在定性上是一致的，并且大大扩展了PROMISE实验的可实现参数范围。我们发现，随着雷诺数的增加，缺陷积累并成长为湍流，但动量输运的尺度很弱。
The magnetorotational instability (MRI) is thought to be a powerful source of turbulence and momentum transport in astrophysical accretion discs, but obtaining observational evidence of its operation is challenging. Recently, laboratory experiments of Taylor-Couette flow with externally imposed axial and azimuthal magnetic fields have revealed the kinematic and dynamic properties of the MRI close to the instability onset. While good agreement was found with linear stability analyses, little is known about the transition to turbulence and transport properties of the MRI. We here report on a numerical investigation of the MRI with an imposed azimuthal magnetic field. We show that the laminar Taylor-Couette flow becomes unstable to a wave rotating in the azimuthal direction and standing in the axial direction via a supercritical Hopf bifurcation. Subsequently, the flow features a catastrophic transition to spatio-temporal defects which is mediated by a subcritical subharmonic Hopf bifurcation. Our results are in qualitative agreement with the PROMISE experiment and dramatically extend their realizable parameter range. We find that as the Reynolds number increases defects accumulate and grow into turbulence, yet the momentum transport scales weakly.