[FLASH-USERS] Problems with 2.5D cylindrical disk using FLASH 4.2.2 unsplit solver

[Klaus Weide]

On Tue, 5 May 2015, Andrea Derdzinski wrote:

> I noticed that FLASH has an option to set hydrostatic boundary conditions,
> and that there are two versions (Flash2HSE and Flash3HSE) but I couldn't
> find any documentation that described the difference between these two
> versions. Can anyone explain why the Flash3 implementation of hydrostatic
> boundary conditions may be better than the Flash2 one?
> Do they both use the same method described in Zingale et al 2002?
> http://adsabs.harvard.edu/abs/2002ApJS..143..539Z)?

Andrea,

The Flash3HSE boundary conditions implement the method described in 
Zingale et al 2002 (or at least one of the variants described there.)

I ported the Flash2HSE boundary conditions at some point (earlier) from 
the FLASH2 code, but without much testing - in general I would trust
the Flash3HSE version more where both are applicable. Flash3HSE boundaries 
(or code equivalent to them) have been used in production simulations
with FLASH3 or FLASH4 at the Flash Center, which is not true for the
Flash2HSE version.

> While the current HSE boundary conditions assume uniform gravity, I am
> interested in implementing hydrostatic boundary conditions that work with
> spatially dependent gravitational acceleration.

The Flash3HSE bcs apply only to Constant gravity; the Flash2HSE variant
tries to be more general, by relying on a routine Gravity_accelAtCoords()
to get the accelerations (which could in principle be in arbitrary
directions). As I said the latter isn't much tested AFAIK; moreover,
implementations of Gravity_accelAtCoords() are only used for these
kinds of boundary conditions and are therefore not much tested either
(or could even be unimplemented for some implementations of the 
Gravity unit).

The best source for more information is probably the source code under

 Grid/GridBoundaryConditions/Flash3HSE ,
 Grid/GridBoundaryConditions/Flash2HSE ,

respectively.


Klaus