Magnetic Helicity Dissipation and Production in an Ideal MHD Code
Magnetic Helicity Dissipation and Production in an Ideal MHD Code
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DOI：
10.3847/1538-4357/ab5e7f
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发表时间：
2019-10
期刊：
影响因子：
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通讯作者：
A. Brandenburg;E. Scannapieco
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文献类型：
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作者：
A. Brandenburg;E. Scannapieco
我们通过使用发散清理八波方法用 FLASH 代码求解理想磁流体动力学 (MHD) 方程来研究周期域中的湍流螺旋发电机，并将我们的结果与使用 Pencil 代码的直接数值模拟 (DNS) 进行比较。在低分辨率下，FLASH 通过产生 DNS 所期望的大尺度磁场来定性地再现 DNS 结果，但在更高分辨率下，无法获得大尺度磁场。在产生大范围磁场的所有情况下，理想的 MHD 结果在小范围内产生的功率太少。因此，小规模当前的螺旋度与 DNS 的螺旋度相比太小。由此产生的净电流螺旋度始终具有错误的符号，并且其统计平均值在后期也不会接近零，正如 DNS 所期望的那样。我们的结果对于使用理想 MHD 代码对恒星和星系磁性进行天体物理发电机模拟具有重要意义。
We study a turbulent helical dynamo in a periodic domain by solving the ideal magnetohydrodynamic (MHD) equations with the FLASH code using the divergence-cleaning eight-wave method and compare our results with direct numerical simulations (DNS) using the Pencil Code. At low resolution, FLASH reproduces the DNS results qualitatively by developing the large-scale magnetic field expected from DNS, but at higher resolution, no large-scale magnetic field is obtained. In all those cases in which a large-scale magnetic field is generated, the ideal MHD results yield too little power at small scales. As a consequence, the small-scale current helicity is too small compared with that of the DNS. The resulting net current helicity has then always the wrong sign, and its statistical average also does not approach zero at late times, as expected from the DNS. Our results have implications for astrophysical dynamo simulations of stellar and galactic magnetism using ideal MHD codes.