Astronomy and Astrophysics – Astrophysics
Scientific paper
2008-06-10
Astron. Astrophys. 495, 1-8 (2008)
Astronomy and Astrophysics
Astrophysics
A&A, in press
Scientific paper
10.1051/0004-6361:200810359
We study the dependence of turbulent transport coefficients, such as the components of the $\alpha$ tensor ($\alpha_{ij}$) and the turbulent magnetic diffusivity tensor ($\eta_{ij}$), on shear and magnetic Reynolds number in the presence of helical forcing. We use three-dimensional direct numerical simulations with periodic boundary conditions and measure the turbulent transport coefficients using the kinematic test field method. In all cases the magnetic Prandtl number is taken as unity. We find that with increasing shear the diagonal components of $\alpha_{ij}$ quench, whereas those of $\eta_{ij}$ increase. The antisymmetric parts of both tensors increase with increasing shear. We also propose a simple expression for the turbulent pumping velocity (or $\gamma$ effect). This pumping velocity is proportional to the kinetic helicity of the turbulence and the vorticity of the mean flow. For negative helicity, i.e. for a positive trace of $\alpha_{ij}$, it points in the direction of the mean vorticity, i.e. perpendicular to the plane of the shear flow. Our simulations support this expression for low shear and magnetic Reynolds number. The transport coefficients depend on the wavenumber of the mean flow in a Lorentzian fashion, just as for non-shearing turbulence.
Brandenburg Axel
Käpylä Petri J.
Mitra Dhrubaditya
Tavakol Reza
No associations
LandOfFree
Alpha effect and diffusivity in helical turbulence with shear does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Alpha effect and diffusivity in helical turbulence with shear, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Alpha effect and diffusivity in helical turbulence with shear will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-174739