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July 20, 2011, 04:30 
High pressure residual simpleFoam

#1 
New Member
Luca Barbone
Join Date: Aug 2010
Posts: 2
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Hi all,
I am running a simulation for external aerodynamics with simpleFoam. I am quite confident with my "standard" setup, never had big troubles. But there is one case (same bc, just different geometry) where I have some problem. The solution doesn't look to bad, but I have high residuals mainly for pressure. Can this suggest that there is a problem somewhere? The residuals go incredibly low in the first 50100 iteration, pressure to 0.0005 (usually these simulation converged at 0.008) but then suddenly start increasing. I am trying also with first order and 1 nonOrthoCorrector but it looks similar. I'll paste the output and some setting: without corrector: smoothSolver: Solving for Ux, Initial residual = 9.53135923113133e05, Final residual = 6.40125609233725e06, No Iterations 3 smoothSolver: Solving for Uy, Initial residual = 0.00583292437866579, Final residual = 0.000408635173001429, No Iterations 3 smoothSolver: Solving for Uz, Initial residual = 0.00107172584371381, Final residual = 7.33804021586605e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.370892890676336, Final residual = 0.00805233261805146, No Iterations 2 time step continuity errors : sum local = 8.93727966506124e05, global = 7.38809614603939e07, cumulative = 0.00600977288580794 smoothSolver: Solving for omega, Initial residual = 5.71563590189836e05, Final residual = 5.20189909513911e06, No Iterations 4 smoothSolver: Solving for k, Initial residual = 0.00296034798651617, Final residual = 0.000165450839972275, No Iterations 3 ExecutionTime = 68868.42 s ClockTime = 69068 s with corrector: Time = 1238 smoothSolver: Solving for Ux, Initial residual = 0.000235167399322179, Final residual = 1.49861216273521e05, No Iterations 3 smoothSolver: Solving for Uy, Initial residual = 0.0167873770137804, Final residual = 0.00104310120382418, No Iterations 3 smoothSolver: Solving for Uz, Initial residual = 0.00393616314129379, Final residual = 0.000237925232432727, No Iterations 3 GAMG: Solving for p, Initial residual = 0.479556064779533, Final residual = 0.00355207736688959, No Iterations 3 GAMG: Solving for p, Initial residual = 0.171937712915105, Final residual = 0.00129806088756816, No Iterations 4 time step continuity errors : sum local = 7.17828577284389e05, global = 6.80223237496025e07, cumulative = 0.00594026418728066 smoothSolver: Solving for omega, Initial residual = 8.49925768943358e05, Final residual = 5.65726497999539e06, No Iterations 4 smoothSolver: Solving for k, Initial residual = 0.00579911848397957, Final residual = 0.000283318812986071, No Iterations 3 ExecutionTime = 69734.74 s ClockTime = 69934 s Settings: divSchemes { default Gauss linear; //div(phi, U) Gauss linearUpwindV cellLimited Gauss linear 1; //div(phi,U) Gauss linearUpwindV Gauss linear; div(phi,U) Gauss upwind; div(phi,Ualter) Gauss linearUpwindV cellMDLimited Gauss linear 1; div(phi,k) Gauss upwind; div(phi,kl) Gauss limitedLinear 1; div(phi,epsilon) Gauss limitedLinear 1; div(phi,omega) Gauss upwind; div(phi,R) Gauss upwind; div(R) Gauss linear; div(phi,nuTilda) Gauss limitedLinear 1; div((nuEff*dev(grad(U).T()))) Gauss linear; } SIMPLE { nNonOrthogonalCorrectors 1; pressureImplicitPorousity false; pRefCell 0; pRefValue 0; pdRefCell 0; pdRefValue 0; } solvers { //p GAMG { agglomerator faceAreaPair ; mergeLevels 1 ; cacheAgglomeration true ; nCellsInCoarsestLevel 200 ; tolerance 1e07 ; relTol 0.05 ; smoother GaussSeidel ; nPreSweeps 0 ; nPostSweeps 2 ; nFinestSweeps 2 ; }; p GAMG { agglomerator faceAreaPair ; mergeLevels 1 ; cacheAgglomeration true ; nCellsInCoarsestLevel 200 ; tolerance 1e07 ; relTol 0.01 ; smoother GaussSeidel ; nPreSweeps 0 ; nPostSweeps 2 ; nFinestSweeps 2 ; }; U smoothSolver { smoother GaussSeidel ; tolerance 1e06 ; relTol 0.1 ; }; k smoothSolver { smoother GaussSeidel ; tolerance 1e06 ; relTol 0.1 ; }; kl smoothSolver { smoother GaussSeidel ; tolerance 1e06 ; relTol 0.1 ; }; epsilon smoothSolver { smoother GaussSeidel ; tolerance 1e06 ; relTol 0.1 ; }; R smoothSolver { smoother GaussSeidel ; tolerance 1e06 ; relTol 0.1 ; }; nuTilda smoothSolver { smoother GaussSeidel ; tolerance 1e06 ; relTol 0.1 ; }; omega smoothSolver { smoother GaussSeidel ; tolerance 1e06 ; relTol 0.1 ; }; h smoothSolver { smoother GaussSeidel ; tolerance 1e06 ; relTol 0.1 ; }; T smoothSolver { smoother GaussSeidel ; tolerance 1e06 ; relTol 0.1 ; }; rho PCG { preconditioner DIC ; tolerance 0 ; relTol 0 ; }; } relaxationFactors { p 0.2; pd 0.3; U 0.5; k 0.5; kl 0.7; epsilon 0.7; R 0.7; nuTilda 0.7; omega 0.7; h 0.7; rho 1; } I have tried different under relaxation but if didn't help. I hope someone can help me or suggest somethings! thanks in advance Ciao! Ciccio 

July 21, 2011, 03:41 

#2 
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,880
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Since the setup works in other cases, I would check the mesh.
P.S. It looks like you are using a nonstandard version of simpleFOAM. best,
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Alberto GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image. GeekoCFD 32bit  The 32bit edition of GeekoCFD. GeekoCFD text mode  A smaller version of GeekoCFD, textmode only, with only OpenFOAM. Available in a variety of virtual formats. 

July 25, 2011, 02:56 

#3 
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Luca Barbone
Join Date: Aug 2010
Posts: 2
Rep Power: 0 
Hi Alberto,
Thanks for your advice, actually the mesh was not that bad. Btw I remeshed the geometry with some different parameter and now it works fine. Thanks again, best regards Luca 

July 25, 2011, 03:03 

#4 
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Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,880
Rep Power: 25 
Good to hear it is working. Sometimes a few cells cause the problem, and the solution is not really affected ;)
__________________
Alberto GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image. GeekoCFD 32bit  The 32bit edition of GeekoCFD. GeekoCFD text mode  A smaller version of GeekoCFD, textmode only, with only OpenFOAM. Available in a variety of virtual formats. 

December 27, 2012, 15:07 

#5 
Senior Member
Join Date: Nov 2012
Posts: 168
Rep Power: 3 
Hi All,
I use rhoPimpleFoam (LES) for my simulations. I also use GAMG linear solver to update the pressure, but I found that the the amount of iteration step for pressure is much higher than other quantities. I copy some output here: diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 PIMPLE: iteration 1 DILUPBiCG: Solving for Ux, Initial residual = 0.000161779, Final residual = 1.72098e09, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000254413, Final residual = 2.84039e09, No Iterations 1 GAMG: Solving for p, Initial residual = 0.140828, Final residual = 9.19848e07, No Iterations 97 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors (Low Ma): sum local = 1.24031e11, global = 8.09049e14, cumulative = 6.05813e11 rho max/min : 1.8221 1.1966 The setting for the pressure linear solver is as follows: "(p)" { solver GAMG; preconditioner FDIC; tolerance 1e6; relTol 0; nCellsInCoarsestLevel 100; agglomerator faceAreaPair; mergeLevels 1; smoother GaussSeidel; nPreSweeps 0; nPostSweeps 1; nFinestSweeps 1; } The question I would like to ask is: why the pressure should be iterate so many times compared to others? How can it be reduced to a reassonable level without loss of accuracy? Does anybody know something about this? I really appreciate it if some can give me some help. regards, H 

March 5, 2013, 21:20 

#7 
Member
Nikesh Bhattarai
Join Date: Nov 2011
Location: Daejeon, South Korea
Posts: 45
Rep Power: 3 
Hii there,
I have a similar problem. I am running RANS simulation for a 2Dflat plate case. I had also posted this problem earlier but unable to hear from anybody about it. If you have managed to figure it out, would anybody here plz tell me about it? Initial Residual for p too high! This is the link I had posted to earlier. My initial presiduals are higher than the others Ux,Uy,k,omega, etc.. 

Tags 
convergence issues, openfoam 1.6, simplefoam 
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