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Convergence issues with RANS, Axisymmetric: SU2 has diverged (NaN detected).

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Old   June 12, 2024, 11:37
Post Convergence issues with RANS, Axisymmetric: SU2 has diverged (NaN detected).
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Hello,
I am little new to open source codes, I would really appreaciate some input on this issue,

So, I have been trying to simulate a RANS 2d external turbojet engine flow, using an axisymmetric domain, of 923k elements for a domain spread across 5m by 3m, with SST turbulence model, I have not implemented any wall functions, as it keeps throwing me warnings of y+<5 or y+<1 points.

but when I turn of the wall functions, after a while the solution solves and diverges.
or is it because of the CFL number being 15 being a bit higher....not sure what exactly is causing the divergence.

As you can see from the txt file, it runs upto 800 iterations and diverges, I dont know if my mesh is not fine enough or if i should use a coarser mesh, or is there some configuration issue within the convergence parameters or boundary conditions, I have also attached a velcity contour that I visualized before it diverged, the jet velocity and mach number are within the anticipated range (which gives me a hope that the boundary conditions are right..), I dont know why the simulation diverges still.

I have also attached my .cfg file under the name of "forum.txt".

I am running on 6 cores in mpi on my laptop.

Thankyou!!
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File Type: jpg Screenshot 2024-06-12 110716.jpg (30.7 KB, 14 views)
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File Type: txt solver_output_Su2_with error_.txt (122.2 KB, 3 views)
File Type: txt forum.txt (26.5 KB, 1 views)
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Old   June 12, 2024, 13:31
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Hi, can you share the mesh as well?
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Old   June 12, 2024, 13:57
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Here is the mesh, around the farfield and near the jet, I am able to attach only attach images, since the forum has only certain file types allowed for uploading.
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File Type: jpg mesh nearfield.jpg (80.9 KB, 11 views)
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Old   June 12, 2024, 17:50
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I mean as a file, so I can run it...


By the way, it looks really really fine, you can probably reduce the number of cells by a lot. That is also what the warning message is telling you: the mesh is so fine that the wall model is switched off because you are fully resolving the boundary layer.
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Old   June 13, 2024, 09:08
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I think you maybe right, so I tried it with a coarser mesh, and I activated Standard Wall Functions, and the solution still seems to be diverging because it says something like..

| 81| -3.278009| -0.867095| -0.862354| 2.054079|
Warning: Computation of wall coefficients (y+) did not converge in 1 points.
Warning: y+ < 5 in 126 points, for which the wall model is not active.
Warning: Computation of wall coefficients (y+) did not converge in 1 points.
Warning: y+ < 5 in 128 points, for which the wall model is not active.
Warning: T_Wall < 0

I have attached the link to the coarser mesh and the .txt file of the new error herewith,


https://drive.google.com/file/d/1Zz1...ew?usp=sharing

with the coarser mesh, it crashes (diverges) sooner...

Thankyou for your time!!
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File Type: jpg mesh farfieldpng.jpg (194.6 KB, 10 views)
File Type: jpg mesh nearfield.jpg (121.7 KB, 5 views)
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File Type: txt diverging solution log.txt (38.3 KB, 0 views)

Last edited by Vaths; June 13, 2024 at 10:11.
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