Strangeness in Clump Simulations

In order to figure out what is going on with these clumps, I am simplifying the problem to 1 moving clump. We will also be looking at a clump that is initialized in a moving ambient.

Here is the run with all of the original parameters. This uses Z cooling, 80 cells per rclump (4 levels of AMR), Hvisc, and lapplydiffusion are on. Additionally, interporder = 2, lcharlimiters is on, lrestartonpressureprotections and lrestartondensityprotections are both off, and cfl_vars = 1, 0.5, 0.5.

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Test Runs

Here are all the models we talked about yesterday. They all have an effective/actual resolution of 80 cells/rclump.

  • Zcool/nocool, AMR/fixed models are self-explanatory
  • lower cooling = all densities decreased by factor of 10
  • lower contrast = clump density decreased by factor of 50
  • increase diffusion = increased DIFF_ALPHA in solver.data from 0.1 to 0.2
Model Zcool, AMR (orig) Zcool, fixed nocool, AMR nocool, fixed
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Model Zcool, AMR (orig) lower cooling lower contrast increase diffusion
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My thoughts:

  • Zcool, fixed still shows the weird stuff at the head of the clump. It starts off symmetric, but then develops asymmetries which is odd. Thus, it would appear that the AMR is not seeding any instabilities.
  • nocool, AMR/fixed both look better but not perfect. So although much of the problem may be caused by the cooling, I may still need to add some diffusion to get rid of the problem entirely.
  • lowering the cooling by lowering the density everywhere helped. I suspect that not resolving the cooling length may directly lead to the instabilities, or it causes pressure protections that lead to the instabilities. One thing to try is to turn on restarts for pressure protections.
  • lowering the contrast by lowering the clump density did not help. The clump was destroyed much more easily, so it's hard to draw any useful conclusions from this run.
  • increasing the diffusion helped a lot. This run looks nice and smooth. We just have to ask ourselves at what point does adding more diffusion become nonphysical.


UPDATE

Tried turning on restarts for pressure protections. Restarts are triggered almost immediately and often. This will prevent the run from ever finishing, so I had to stop it. I don't see any nans, so it is the protections are presumably caused by very strong cooling that brings the temperature below the mintemp of 1d-10. Perhaps increased resolution could help, or lowering the mintemp and/or raising the floortemp.

They are being triggered at the point (-0.41, 9.12) which is near the lower left edge of the clump. Maybe there is something with the softening or refinement buffering that might help.

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