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Outlet behaves like solid wall

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Old   September 14, 2020, 12:20
Default Outlet behaves like solid wall
  #1
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Harald Radlwimmer
Join Date: Sep 2020
Location: Vienna, Austria
Posts: 5
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Hello,

earlier this year, I started using OpenFOAM at work. Now, I reached the point, where I need assistance.

Currently, I got stuck with the correct definition of my problem's outlet boundary conditions.

My test case has the following setup:

  • axis-symmetric case (see 1-geom.png):
    • chamber (D = 25 mm) with small high-pressure/temperature region,
    • filter,
    • surrounding area
  • initial conditions (see 2-initial-p.png and 2-initial-T.png):
    • air
    • p0 = 1e+05 Pa
    • T0 = 300 K
    • chamber (high temperature/pressure region)
      • air
      • p_region = 20e+05 Pa
      • T_region = 1600 K
    • filter (Darcy-Forchheimer)
  • outlet patches
    • front,
    • right
  • solver
    • rhoPimpleFoam

Currently, my outlet patches seem to behave like solid walls. This understanding comes from the observation of a reflection from the front-patch (see 3-U.png and 4-U.png). However, that is not what I want. Actually, the outlet patch should be perfectly permeable and, therefore, only cut away everything from the environment, which I do not want to simulate.


Unfortunately, I could not find the solution myself (RAS-tutorials, foamInfo, etc.). Please, take a look at my outlet boundary conditions; can you find an obvious failure?

Code:
alphat:


"(front|right)"// outlet
  {
type calculated; value uniform 0;
}
Code:
 k:


 "(front|right)"// outlet
 {
type inletOutlet; inletValue uniform 1e-5; value uniform 1e-5;
}
Code:
 nut:


 "(front|right)"// outlet
 {
type calculated; value uniform 0;
}
Code:
omega:


 "(front|right)"// outlet
  {
type inletOutlet; value uniform 1; inletValue uniform 1;
}
Code:
p:


 "(front|right)"// outlet
  {
type fixedValue; value uniform 1e+5;
}
Code:
T:

 "(front|right)"// outlet
  {
type inletOutlet; value uniform 300; inletValue uniform 300;
}
Code:
 U:


 "(front|right)"// outlet
  {
type pressureInletOutletVelocity; value uniform (0 0 0); inletValue uniform (0 0 0);
}
Let me know if I need to provide some additional information.

Harald
Attached Images
File Type: png 1-geom.png (50.3 KB, 8 views)
File Type: jpg 2-initial-p.jpg (37.5 KB, 7 views)
File Type: jpg 2-initial-T.jpg (33.4 KB, 7 views)
File Type: jpg 3-U.jpg (44.3 KB, 10 views)
File Type: jpg 4-U.jpg (55.2 KB, 11 views)
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Old   September 16, 2020, 06:46
Default Setting pressure outlet BC to waveTransmissive helped
  #2
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Harald Radlwimmer
Join Date: Sep 2020
Location: Vienna, Austria
Posts: 5
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Today, I found a solution for my problem with help of foamInfo. It seems that changing the outlet boundary condition of the pressure from fixedValue to waveTransmissive does the job (see 5-U.png,6-U.png).

The new outlet BC reads:

Code:
p:

"(right|front)"// outlet
{
type waveTransmissive; gamma 1.4;
}
Attached Images
File Type: png 5-U.png (74.4 KB, 6 views)
File Type: png 6-U.png (75.1 KB, 5 views)
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