simplefoam omega convergence problem

simplefoam · August 12, 2013, 05:54

Hello, im working on a external aerodynamic 3d case with simplefoam, with the k omega sst model for the turbulence.

Ive got a question about relaxation factors, cause along the simulation, with linearupwind, i dont get the convergence of the residuals for the omega unless i get the relaxation factor to 0.001 (for omega)

How relaxation factors works?

Can I play modifying them without any restriction?

i-ve attached a figure where i get the omega relaxation factor modified from 0.01 to 0.7...and then to 0.001..

is this correct?

Thanks for your help, im quite novel and very often dont know how these things worls

miro2000 · August 12, 2013, 07:26

Hi!

I'm working on something similar. What are your boundary conditions, free stream velocity? What is your Re? Are you using wall functions?

How did you make your mesh? What is your Y+?

- miro

simplefoam · August 12, 2013, 10:31

HI, on BC i put fixed value, since with freestream i've never got convergence in 3d cases. y+ is about 40 or 50.

My doubts come about the relaxation factors

miro2000 · August 12, 2013, 14:45

Well, I'm not an experienced foamer but i think 1e-3 is pretty low. But I don't think that means your solution is wrong.. However, it should not be necessary to set relaxation factor so low.

In other words, something is wrong with your case. And this is probably it:

Checking geometry...
Overall domain bounding box (-10 0 -10.3) (10 20 10.3)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (7.45683e-16 3.30144e-16 -2.68288e-16) OK.
***High aspect ratio cells found, Max aspect ratio: 804747, number of cells 23310
<<Writing 23310 cells with high aspect ratio to set highAspectRatioCells
Minimum face area = 5.51009e-09. Maximum face area = 9.67452. Face area magnitudes OK.
Min volume = 1.87009e-11. Max volume = 13.563. Total volume = 7321.49. Cell volumes OK.
Mesh non-orthogonality Max: 84.0764 average: 14.1312
*Number of severely non-orthogonal faces: 2520.
Non-orthogonality check OK.
<<Writing 2520 non-orthogonal faces to set nonOrthoFaces
Face pyramids OK.
Max skewness = 0.848689 OK.
Coupled point location match (average 0) OK.

Failed 1 mesh checks.

End

You should fix this first and then look for other problems (maybe in BC).
Cheers,
- miro

simplefoam · August 13, 2013, 06:31

i think mesh is not the problem, because another case meshed very similar with snappy (ok with the mesh), gets ths same results.

anyway, is it bad to put relaxation factor on 0.01???

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August 12, 2013, 07:26		#2
miro2000 Member Miro Join Date: Jan 2013 Location: Europe Posts: 51 Rep Power: 13	Hi! I'm working on something similar. What are your boundary conditions, free stream velocity? What is your Re? Are you using wall functions? How did you make your mesh? What is your Y+? - miro

August 12, 2013, 10:31		#3
simplefoam New Member Pepe Perez Join Date: Aug 2013 Posts: 7 Rep Power: 13	HI, on BC i put fixed value, since with freestream i've never got convergence in 3d cases. y+ is about 40 or 50. My doubts come about the relaxation factors

August 12, 2013, 14:45		#4
miro2000 Member Miro Join Date: Jan 2013 Location: Europe Posts: 51 Rep Power: 13	Well, I'm not an experienced foamer but i think 1e-3 is pretty low. But I don't think that means your solution is wrong.. However, it should not be necessary to set relaxation factor so low. In other words, something is wrong with your case. And this is probably it: Checking geometry... Overall domain bounding box (-10 0 -10.3) (10 20 10.3) Mesh (non-empty, non-wedge) directions (1 1 1) Mesh (non-empty) directions (1 1 1) Boundary openness (7.45683e-16 3.30144e-16 -2.68288e-16) OK. **High aspect ratio cells found, Max aspect ratio: 804747, number of cells 23310 <<Writing 23310 cells with high aspect ratio to set highAspectRatioCells Minimum face area = 5.51009e-09. Maximum face area = 9.67452. Face area magnitudes OK. Min volume = 1.87009e-11. Max volume = 13.563. Total volume = 7321.49. Cell volumes OK. Mesh non-orthogonality Max: 84.0764 average: 14.1312 Number of severely non-orthogonal faces: 2520. Non-orthogonality check OK. <<Writing 2520 non-orthogonal faces to set nonOrthoFaces Face pyramids OK. Max skewness = 0.848689 OK. Coupled point location match (average 0) OK. Failed 1 mesh checks. End You should fix this first and then look for other problems (maybe in BC). Cheers, - miro

August 13, 2013, 06:31		#5
simplefoam New Member Pepe Perez Join Date: Aug 2013 Posts: 7 Rep Power: 13	i think mesh is not the problem, because another case meshed very similar with snappy (ok with the mesh), gets ths same results. anyway, is it bad to put relaxation factor on 0.01???