Central disk, test 3

  • More time resolution than tests 2* and 2.1*
  • particle refinement, which is faster than the amr
  • again*, dens contrast=106, temp=1000K
  • the disk has been rotated by theta=pi/2.
  • rdisk=2 cu (=20AU; rdisk=1cu in test 2 and 2.1*)
  • disk height=2rsoft (it was .75rsoft in test2 & 2.1*). This increase of disk height seems to reduced the length of the central warped region in comparison with tests 2 & 2.1*.
  • periodic BC (note that the domain goes from -6 to 6cu (1cu=10AU), so the disk is till far from the boundary)

The vertical expansion has a velocity ~11.4km/s, which seems reasonable.

Density movie: ​http://www.pas.rochester.edu/~martinhe/2011/binary/3feb12-955.gif

Poloidal velocity movie [mach] ​http://www.pas.rochester.edu/~martinhe/2011/binary/3feb12-1050.gif

The poloidal velocity movie shows the gas located at r ~ < rsoft is quickly pulled towards the particle. Note this is not the ambient gas. This forms a thin -2dx wide-, small central region with colliding Mach 14 flows.http://www.pas.rochester.edu/~martinhe/2011/binary/polVel1-0040.png
Shortly after, asymmetries, likely related to grid resolution and/or numerical diffusion, develop and produce shear. The effect grows in time. This seems to cause the early central warping. It doesn't make sense to me that this central region doesn't precess; I'd expect it to rotate about the disk ang mom axis, even if at a slower speed than the Keplerian one at r >~ rsoft.http://www.pas.rochester.edu/~martinhe/2011/binary/polVel1-0075.png.

The fact that we see central non-precessing warping also for a disk that rotates about the x-axis (and not about the z-axis as in previous tests*), suggests there are no grid geometry bugs. Jonathan has found the same in his own, different, exploratory central disk tests. Still I'm now running a test with an inclination angle of 10o, as suggested by Jonathan.

It's premature to say whether this instability will affect disk material located at r >> rsoft.

*​https://clover.pas.rochester.edu/trac/astrobear/blog/martinhe01292012

Comments

1. martinhe -- 13 years ago

Our isothermal disks do not rotate like solid bodies. As the gas in the center orbits it's pushed up and down by plane symmetric pressure gradients. Otherwise a slice thought a solid rotating disk should show oscillations of the core. I.e.:

I've cut the disk in two and I'm showing both halves face-on. The core is asymmetric with respect to the vertical axis but has plane (mirror) symmetry. Thus if the diks rotated like a solid body with respect to the vertical axis the top and bottom halves should switch places after one orbit. We don't see this.http://www.pas.rochester.edu/~martinhe/2011/binary/halves.png