Dear Arash,

For a subsonic outflow there is one incoming characteristic wave that needs to be computed somehow.
So far I have been using the PressureOutflowNonReflectiveBC setting the farfield static pressure.
I have not tried personally yet, but another option would be to try the RiemannInvariantBC.
Another alternative is to add a sponge layer at the outflow.

I hope this helps.

Cheers,
Giacomo


On Thu, Jan 3, 2019 at 9:49 AM Arash Nouri <nouri.aarash@gmail.com> wrote:

Hi all,

 

Happy new year!

 

I need a kind of zero gradient boundary condition (BC) for the compressible flow solver. As Neumann BC is not implemented for “LDGNS,”  I tried using ExtrapOrder0 BC, but I got oscillations on this boundary.

 

In my 2D simulation I have one Dirichlet and one ExtrapOrder0 BCs as the input and output of my domain and two Symmetry BCs on the top and bottom. The Mach number is very small (~0.001). Is this combination OK for the compressible flow solver? Do you suggest any other option instead of  ExtrapOrder0 or Dirichlet BCs?

 

Thanks in advance,

Arash

 

-----------------------------

Arash G. Nouri

Research Scientist

1127 Benedum Hall

Mechanical Engineering and Materials Science 

University of Pittsburgh

 

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