[FLASH-USERS] Diode BC in 1D allowing mass-inflow

[Matthew Gilmer]

Hi all,
I'm simulating Pair-Instability Supernovae in 1, 2, and 3 dimensions. I
began using the diode BC for the outer boundary because, when using the
outflow BC, I was getting a lot of mass-inflow, so much at times that it
caused a pre-mature and extra strong collapse to a BH (for model masses
which are within the range predicted to explode as PISNe). The diode BC has
worked for the most part, but there is still slow mass-inflow. Some of my
models need to be mapped into FLASH a bit earlier in stellar evolution than
normal, so this mass-inflow continues for a few tens of thousands of
seconds before the core collapses. At this point, as much as 6 solar masses
have been added to the simulation from the outer boundary (for a star of
about 120 solar masses). I think that this is a source of uncertainty too
big to ignore and I'd like to be rid of it.

Although the mass comes in from the outer boundary, I'm inclined to believe
that it might have something to do with the reflecting inner BC. I think
this because the diode BC has done it's job (allowing NO mass inflow) when
I simulate a 3D cartesian cube (all boundaries being diode). In 2D
cylindrical simulations, however, I have the same problem, and I'm using a
reflecting BC for the inner r-axis boundary.

All simulations were done with the 3rd order unsplit hydro solver in FLASH
version 4.3 with the default Paramesh4dev amr grid.

I'd like to know if anybody has experienced a problem like this before, and
if so, what they have tried to combat the issue.

Thanks,
Matt Gilmer
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