Berera Arjun, Linkmann Moritz
SUPA, School of Physics and Astronomy, University of Edinburgh, Peter Guthrie Tait Road EH9 3FD, United Kingdom.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Oct;90(4):041003. doi: 10.1103/PhysRevE.90.041003. Epub 2014 Oct 22.
Ensemble-averaged high resolution direct numerical simulations of reverse spectral transfer are presented, extending on the many single realization numerical studies done up to now. This identifies this type of spectral transfer as a statistical property of magnetohydrodynamic turbulence and thus permits reliable numerical exploration of its dynamics. The magnetic energy decay exponent from these ensemble runs has been determined to be nE=(0.47±0.03)+(13.9±0.8)/Rλ for initially helical magnetic fields. We show that even after removing the Lorentz force term in the momentum equation, thus decoupling it from the induction equation, reverse spectral transfer still persists. The induction equation is now linear with an externally imposed velocity field, thus amenable to numerous analysis techniques. A new door has opened for analyzing reverse spectral transfer, with various ideas discussed.
本文给出了反向谱传递的系综平均高分辨率直接数值模拟结果，拓展了迄今为止众多单样本数值研究的成果。这将此类谱传递确定为磁流体动力学湍流的一种统计特性，从而能够对其动力学进行可靠的数值探索。对于初始螺旋磁场，从这些系综模拟中确定的磁能衰减指数为(n_E = (0.47 \pm 0.03) + (13.9 \pm 0.8)/R_{\lambda})。我们表明，即使在动量方程中去除洛伦兹力项，从而使其与感应方程解耦之后，反向谱传递仍然存在。感应方程现在对于外部施加的速度场是线性的，因此适用于众多分析技术。为分析反向谱传递打开了一扇新的大门，并讨论了各种相关想法。
