黏性各向异性磁流体Kelvin-Helmholtz不稳定性:二维数值研究

Kelvin-Helmholtz instability in anisotropic viscous magnetized fluid

利用corner transport upwind和constrained transport算法求解非理想磁流体动力学方程组,对匀强平行磁场作用下,黏性各向异性等离子体自由剪切层中的Kelvin-Helmholtz不稳定性进行了数值模拟.从流动结构、涡结构演化、磁场分布、横向磁压力、抗弯磁张力等角度对各向同性和各向异性黏性算例结果进行了讨论,分析了黏性各向异性对Kelvin-Helmholtz不稳定性的影响.结果表明,黏性各向异性比黏性各向同性更利于流动的稳定.其稳定性作用是由于磁感线方向上剪切速率降低导致界面卷起程度和圈数的降低,并使卷起结构中小涡产生增殖、合并,破坏了涡的常规增长,从而导致流动的稳定.黏性各向异性对横向磁压力的影响比对抗弯磁张力更大.

Kelvin-Helmholtz instability in anisotropic viscous fluid with uniform density in the presence of magnetic field is simulated through solving the non-ideal magnetohydrodynamic equations.The magnetic field is uniform and parallel to the stream.The magnetohydrodynamic equations are solved by corner transport upwind algorithm and constrained transport algorithm.In this paper,the influence of viscous anisotropy on KelvinHelmholtz instability is studied.The viscous anisotropy is embodied in the direction of the magnetic field,that is,viscosity parallel to the direction of the magnetic field line is much larger than that in the other directions.The results in the isotropic and the anisotropic viscous cases are compared from the aspects of flow structure,vortex evolution,and magnetic field distribution.It shows that the viscous anisotropy is more advantageous to the stability in a magnetized shear layer than the viscous isotropy.The flow structure evolves similarly in large scales but vortices evolve differently in small scales.Due to the decrease of the shear rate in the direction of the magnetic field lines,the rolling-up degree of interface and the number of laps decrease;the multiplication and merging of small vortices in the rolled-up structure destroy the regular growth of the vortex,which contributes to the stability of the flow.The increase of the magnetic energy at the sheared interface slows down effectively by the viscous anisotropy,which weakens the growth of the transverse magnetic pressure and anti-bending magnetic tension.However,viscous anisotropy shows much greater influence on the transverse magnetic pressure than on the anti-bending magnetic tension.The total enstrophy decreases slowly in viscous isotropy and anisotropy case.It increases quickly in late time in the former case,but is heavily suppressed in the latter case.