# simplefoam omega convergence problem

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August 12, 2013, 04:54
simplefoam omega convergence problem
#1
New Member

Pepe Perez
Join Date: Aug 2013
Posts: 7
Rep Power: 5
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
Attached Images
 residuals2.png (15.1 KB, 22 views)
Attached Files
 3dwingcasesimplefoam.zip (31.2 KB, 6 views)

 August 12, 2013, 06:26 #2 Member   Miro Join Date: Jan 2013 Location: Europe Posts: 51 Rep Power: 5 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, 09:31 #3 New Member   Pepe Perez Join Date: Aug 2013 Posts: 7 Rep Power: 5 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, 13:45 #4 Member   Miro Join Date: Jan 2013 Location: Europe Posts: 51 Rep Power: 5 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 <

 August 13, 2013, 05:31 #5 New Member   Pepe Perez Join Date: Aug 2013 Posts: 7 Rep Power: 5 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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