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

E-mail: arash.nouri@pitt.edu <arn36@pitt.edu>

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