Transport properties of Keplerian flows in extended local domains with no imposed field

Abstract

We compare transport statistics of elongated incompressible shearing boxes for different Reynolds and magnetic Prandtl numbers, $Re$ and $Pm$, and aspect ratios, $L_z/L_x$. We find that at fixed aspect ratio $L_z/L_x=4$ and $Re=10,000$, the turbulent stresses for $Pm\lesssim 1$ do not show considerable variation and follow a power law $\sim P{m}^{3/2}$ for $Pm>1$. This is qualitatively consistent with previous results based on net imposed flux and small box $L_z/L_x\sim 1$ simulations but the power law exponent is different. The saturated level of stresses, the ratio of Maxwell stress to the magnetic energy and Reynolds to Maxwell stress ratio are roughly invariant as $L_z/L_x$ is increased. For cases where the boxes are elongated in both the azimuth and vertical direction, the transport coefficient $\alpha \in [0.1,1.0]$ that is $10-100$ times larger than the case with $L_y/L_x=2$ and large $L_z/L_x$. Overall, our results suggest that the saturated state of turbulence is sensitive to both dissipation coefficients and aspect ratio (both $L_z/L_x$, $L_y/L_x$) motivating further work on this problem.

6 pages, 7 figures