Turbulent stresses as a function of shear rate in a local disk model

TL;DR

This paper investigates how turbulent stresses in accretion disks depend on shear rate using local numerical models driven by the magnetorotational instability, and compares results with a closure model.

Contribution

It introduces a local disk turbulence model with five parameters and evaluates its ability to reproduce shear rate effects observed in simulations.

Findings

Turbulent stress ratio varies strongly with shear rate.

The closure model qualitatively captures the behavior of turbulent stresses.

Magnetic to kinetic energy ratio depends on shear rate.

Abstract

We present local numerical models of accretion disk turbulence driven by the magnetorotational instability with varying shear rate. The resulting turbulent stresses are compared with predictions of a closure model in which triple correlations are modelled in terms of quadratic correlations. This local model uses five nondimensional parameters to describe the properties of the flow. We attempt to determine these closure parameters for our simulations and find that the model does produce qualitatively correct behaviour. In addition, we present results concerning the shear rate dependency of the magnetic to kinetic energy ratio. We find both the turbulent stress ratio and the total stress to be strongly dependent on the shear rate.