Anisotropy of magnetohydrodynamic turbulence at low magnetic Reynolds number

Abstract

Turbulent fluctuations in magnetohydrodynamic flows are known to become anisotropic under the action of a sufficiently strong magnetic field. We investigate this phenomenon in the case of low magnetic Reynolds number using direct numerical simulations and large eddy simulations of a forced flow in a periodic box. A series of simulations is performed with different strengths of the magnetic field, varying Reynolds number, and two types of forcing, one of which is isotropic and the other limited to two-dimensional flow modes. We find that both the velocity anisotropy ͑difference in the relative amplitude of the velocity components͒ and the anisotropy of the velocity gradients are predominantly determined by the value of the magnetic interaction parameter. The effects of the Reynolds number and the type of forcing are much weaker. We also find that the anisotropy varies only slightly with the length scale.

Smagorinsky constant in LES modeling of anisotropic MHD turbulence

“…The main results of [6] deal with the transformation of turbulent fluctuations at intermediate and small length scales. The scale-dependent gradient anisotropy was estimated using…”

“…A detailed study of the anisotropy of homogeneous MHD turbulence at low R m was conducted in [6]. DNS and LES computations were performed in a wide range of Re and N .…”

“…We focus on MHD turbulence far from the walls and consider the implications of the special properties resulting from the presence of the Lorentz force term in (2) for large-eddy simulations. Such properties have been relatively thoroughly studied in analytical, experimental, and numerical works (see, for example, [3][4][5][6]). It has been understood that in unbounded flows the direct effect of the magnetic field is twofold.…”

Directional and scale-dependent statistics of quasi-static magnetohydrodynamic turbulence

“…Quasi-static MHD turbulence has been studied by means of direct numerical simulation (DNS) and different tools to quantify the anisotropy have been developed so far [3]. Using energy spectra in Fourier space, it is shown that the anisotropy is persistent at small scale [4][5][6]. These spectral analyses, while capturing the multiscale character, cannot quantify the spatially intermittent nature of the flows.…”

Instability and transition to turbulence in a free shear layer affected by a parallel magnetic field

“…The effect can also be seen in the power spectra in figure 10(c). High-q x modes are suppressed by the magnetic field and the spectrum takes the anisotropic form typical for MHD turbulence at moderate to high N (Zikanov & Thess 1998;Vorobev et al 2005). The flow evolution in the case of the one-wave initial conditions has some features reminiscent of the non-magnetic scenario (see, for example, Metcalfe et al 1987;Rogers & Moser 1992, 1993.…”