[FLASH-USERS] [EXT] outflow boundary conditions

[Eddie Hansen]

The grid has what we call 'guard cells' outside of the domain. These are
given values according to the desired BC. Let imax be the last cell inside
the domain in the x-direction. An outflow BC on the upper-x boundary would
set guard cells as follows:

U(imax+1) = U(imax)

where U is the array of all variables (density, velocity, pressure, etc.).
Thus the gradients across the boundary are zero, and anything that flows up
to the boundary, including shocks, will keep going and leave the domain.

On Tue, Jul 13, 2021, 2:54 AM Maksim Kozlov <maksim.kozlov at nu.edu.kz> wrote:

> Dear flash users,
> I would really appreciate it if somebody explains to me the exact meaning
> of outflow boundary conditions in FLASH. The only explanation that I was
> able to find in the user's manual is that outflow boundary conditions mean
> zero gradient boundary conditions that allow shock to leave the domain.
> Could you please explain to me the gradient of what is zero and why it
> allows shock to leave the domain. How does flash assign values of pressure,
> density, velocity and energy on the outflow boundaries?
> thank you very much
> Maksim Kozlov
>
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