Convergence

Luiz Eduardo Bittencourt Sampaio (Sampaio)

Dear Sirs,

I know OpenFOAM is tunned to achieve better performance than comercial codes in good meshes, and I can gladly see it do so.

However I am having some problems with convergence with kepsilon model (also tried LRR, and a v2f I implemented myself - still testing). I dont think my mesh is that bad, but I would like to tunne my parameters so that I get a more robust solver.

Does anyone out there has any guidelines on schemes and parameters towards a more robust solver?

I have observed some issues regarding kepsilon, for instance:

1- if I set the tolerance for k and epsilon equation to 10^-5, my solution blows up. Setting it to 0.001 corrects it, but it limits my accuracy to 0.001, where I would like it to be much better.

2- velocity usually converge faster, while pressure residuals stagnate at some level. Is there a way to modify those parameters so that pressure converges faster?

3- I tried to use other solvers, since I thought I might be having trouble because of coupling between the equations (mostly in my v2f implementation). Is it right to say a GaussSeidel solver is more robust when there is a strong coupling than a BICCG? I set number of sweeps to 1 and relative tolerance to 0.999 to guarantee that I was "mixing well" the equations (one sweep for each variable). Is there a misconception? (I know it is slower). Do you think BICCG could do as a good job as GaussSeidel in strongly coupled systems, while still being much faster? (Would you limit the number of iterations the same way I did for GS?)

I apreciate any comments and help.
Luiz