Self‐organization in the two‐dimensional magnetohydrodynamic transverse Kelvin‐Helmholtz instability
Self‐organization in the two‐dimensional magnetohydrodynamic transverse Kelvin‐Helmholtz instability
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二维磁流体动力学横向开尔文-亥姆霍兹不稳定性中的自组织
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发表时间：
1999
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影响因子：
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通讯作者：
A. Miura
中科院分区：
文献类型：
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作者：
A. Miura
对于可压缩等离子体中的二维横向构型，我们对亚快剪切流的开尔文-亥姆霍兹 (K-H) 不稳定性进行了磁流体动力学模拟。模拟表明，在增长最快的涡旋线性增长和随后的非线性饱和之后，这些涡旋很容易受到涡旋配对的影响，这种配对是由于分谐波的增长而发生的。在不稳定性的演化过程中，总动能几乎保持恒定，但由于人工粘度的选择性耗散，熵迅速减小，添加人工粘度是为了防止网格振荡。因此，二维横向K-H不稳定性的非线性演化，特别是涡旋的连续配对，可以很好地描述为非线性和耗散相互作用产生的自组织过程。在不稳定发展的早期阶段之后，动能和平方涡量向长波长级联（逆级联），在波数空间中形成幂律谱。波数空间中的逆级联对应于构型空间中早期小尺度涡流和电流涡流中出现的大的孤立流动涡流和相关的惯性流涡流。模拟运行结束时，动能、平方涡度和磁能的波数空间中的幂律指数（全部在初始流动方向上积分）在中间波数子范围中分别变为 -3.89、-2.08 和 -4.58。
For a two-dimensional transverse configuration in a compressible plasma a magnetohydrodynamic simulation of the Kelvin-Helmholtz (K-H) instability has been performed for a subfast shear flow. The simulation shows that after the linear growth and the subsequent nonlinear saturation of the fastest growing vortices these vortices are susceptible to vortex pairings, which occur because of the growth of subharmonics. The total kinetic energy remains almost constant in the evolution of the instability, but the enstrophy decreases rapidly owing to the selective dissipation by an artificial viscosity, which is added to prevent mesh oscillations. Therefore the nonlinear evolution of the two- dimensional transverse K-H instability, in particular, the successive pairings of vortices, are well described as a self-organization process resulting from the interplay of the nonlinearity and the dissipation. After the early stage of the instability development the kinetic energy and the squared vorticity cascade toward the long wavelength (inverse cascade) to form power law spectra in the wavenumber space. The inverse cascade in the wavenumber space corresponds, in the configuration space, to an emergence of a large isolated flow vortex and an associated eddy of inertia current out of trains of small-scale vortices and current eddies in the early stage. At the end of the simulation run the power law exponents in the wavenumber space of the kinetic energy, the squared vorticity, and the magnetic energy, which are all integrated across the initial flow direction, become -3.89, -2.08, and -4.58, respectively, in the intermediate wavenumber subrange.