Numerical Viscosity - Marvin

I did some simulations with different resolutions to investigate the effects of numerical viscosity at the inner rim of the accretion disk. The simulations show the surface density of the disk and are without magnetic field and outflow. The black circle shows the initial inner rim of the accretion disk (1 pc). I run these simulations for about 10 orbital timescales (at 1 pc).

Animation of the Surface Density, inner 6 pc of the disk, level 2​

Animation of the Surface Density, inner 6 pc of the disk, level 4​

Animation of the Surface Density, inner 6 pc of the disk, level 5​

The first simulation has a resolution of 0.16 pc (level 2) at the location of the inner rim and 0.04 pc (level 4) around the center (approx. the inner 0.2 pc). The disk material moves inwards quickly, probably due to numerical viscosity. At the end of the simulation the inner cavity has almost vanished.

In the second simulation the resolution at the location of the inner rim has changed to 0.04 pc (level 4). The inner rim still moves inwards, but only from 1 pc to 0.8 pc. We also have to consider that the disk and its inner rim have to relax from its initial conditions, as there are large density and pressure gradients at the beginning of the simulation.

The third simulation has a resolution of 0.02 pc (level 5) everywhere in the disk. This looks slightly better than the previous simulation, but qualitatively there is no big difference.

So I think level 4 is an adequate resolution to avoid too large effects due to numerical viscosity.

Surface Density, inner 6 pc of the disk, level 2:

Surface Density, inner 6 pc of the disk, level 4:

Surface Density, inner 6 pc of the disk, level 5:

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