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- - **smoothSolver diverges - solution in using PBiCG solver?**
(*https://www.cfd-online.com/Forums/openfoam-solving/71109-smoothsolver-diverges-solution-using-pbicg-solver.html*)

smoothSolver diverges - solution in using PBiCG solver?Hi all!
I have 2 points to discuss: 1st one: I wrote a heat transfer solver based on pimpleFoam, adding heat transfer equation. I use high Courant numbers (up to 5) to speed up calculations. Flow simulation runs without problems (GAMG solver for pressure, smoothSolvers for U and turbulent parameters). By analogy I used smoothSolver also for TEqn in my solver: Code:
` T` Then I just switched TEqn solver to PBiCG with DILU preconditioner Code:
` T` So what is the reason for such behavior? 2nd point: Why am I using pimpleFoam? I solve more complicated task with solidification and turbulent flow. For some cases I search for steady state. One approache is to use steady state solvers, another - to apply transient or cvazi-transient solvers to reach steady state when solution will become stable. I tried to use simpleFoam just to test such posibility for my task. It reached solution which transient solvers achieve and do not change later, but instanteniously solution deverged! Residuals got a big jump and solution crashed... Am wondering why it happend? Stable solution for that simmetric geometry which I used was assimetric, because there are 3 jets and in 2D they cannot be stable because two zones of low pressure do not have a connection. Is assymethry of solution the case for steady state solver to deverge? So now I an forced to use PISO or PIMPLE technics to solve my problem... But it is time-consuming! So, waiting for your opinion! Have a good day! |

Hello, Dr. Alexander VAKHRUSHEV,
I have met the same situation as you had. Have you got an idea about it? Jackie |

Hi Jackie!
My post was from 2009, since that OpenFOAM improved a lot in numerics. So I do not observe that now in my simulations... Sometimes under-relaxation really helps to avoid simulation from explosion. Cheers, Alexander |

MultigrideHi Dr.Alexander
Can you tell me what the difference is GAMG algorithms algorithms AMG? THANKS |

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