Tridimensional to bidimensional transition in magnetohydrodynamic turbulence with a guide field and kinetic helicity injection
Tridimensional to bidimensional transition in magnetohydrodynamic turbulence with a guide field and kinetic helicity injection
复制标题
具有引导场和动力螺旋注入的磁流体动力湍流的三维到二维转变
DOI：
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发表时间：
2016
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影响因子：
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通讯作者：
P. Mininni
中科院分区：
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作者：
N. E. Sujovolsky;P. Mininni
本文研究了当磁场强度逐渐增大时，仅机械施加的三维磁流体动力流的维数变化。我们使用数值模拟来考虑机械力在流动中注入（或不注入）螺旋度的情况。随着引导场的增大，磁场波动强度随引导场强度的幂律而减小。结果表明，在足够强的引导场条件下，螺旋磁流体流动可以接近二维。在这种情况下，机械能可以经历一个与反级联相容的过程，优先向比强迫尺度更大的尺度转移。螺旋度的存在改变了小磁场波动的谱标度，影响了速度场和速度梯度的统计量。此外，在小尺度上，流动的动力学由直接的螺旋级联控制，这可以用来推导速度场的标度定律。
We study the transition in dimensionality of a three-dimensional magnetohydrodynamic flow forced only mechanically, when the strength of a magnetic guiding field is gradually increased. We use numerical simulations to consider cases in which the mechanical forcing injects (or not) helicity in the flow. As the guiding field is increased, the strength of the magnetic field fluctuations decrease as a power law of the guiding field intensity. We show that for strong enough guiding fields, the helical magnetohydrodynamic flow can become almost two-dimensional. In this case, the mechanical energy can undergo a process compatible with an inverse cascade, being transferred preferentially towards scales larger than the forcing scale. The presence of helicity changes the spectral scaling of the small magnetic field fluctuations, and affects the statistics of the velocity field and of the velocity gradients. Moreover, at small scales the dynamics of the flow becomes dominated by a direct cascade of helicity, which can be used to derive scaling laws for the velocity field.