# High pressure residual simpleFoam

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 July 20, 2011, 04:30 High pressure residual simpleFoam #1 New Member   Luca Barbone Join Date: Aug 2010 Posts: 2 Rep Power: 0 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 50-100 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 = 9.53135923113133e-05, Final residual = 6.40125609233725e-06, 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 = 7.33804021586605e-05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.370892890676336, Final residual = 0.00805233261805146, No Iterations 2 time step continuity errors : sum local = 8.93727966506124e-05, global = -7.38809614603939e-07, cumulative = 0.00600977288580794 smoothSolver: Solving for omega, Initial residual = 5.71563590189836e-05, Final residual = 5.20189909513911e-06, 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 = 1.49861216273521e-05, 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 = 7.17828577284389e-05, global = -6.80223237496025e-07, cumulative = 0.00594026418728066 smoothSolver: Solving for omega, Initial residual = 8.49925768943358e-05, Final residual = 5.65726497999539e-06, 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 1e-07 ; relTol 0.05 ; smoother GaussSeidel ; nPreSweeps 0 ; nPostSweeps 2 ; nFinestSweeps 2 ; }; p GAMG { agglomerator faceAreaPair ; mergeLevels 1 ; cacheAgglomeration true ; nCellsInCoarsestLevel 200 ; tolerance 1e-07 ; relTol 0.01 ; smoother GaussSeidel ; nPreSweeps 0 ; nPostSweeps 2 ; nFinestSweeps 2 ; }; U smoothSolver { smoother GaussSeidel ; tolerance 1e-06 ; relTol 0.1 ; }; k smoothSolver { smoother GaussSeidel ; tolerance 1e-06 ; relTol 0.1 ; }; kl smoothSolver { smoother GaussSeidel ; tolerance 1e-06 ; relTol 0.1 ; }; epsilon smoothSolver { smoother GaussSeidel ; tolerance 1e-06 ; relTol 0.1 ; }; R smoothSolver { smoother GaussSeidel ; tolerance 1e-06 ; relTol 0.1 ; }; nuTilda smoothSolver { smoother GaussSeidel ; tolerance 1e-06 ; relTol 0.1 ; }; omega smoothSolver { smoother GaussSeidel ; tolerance 1e-06 ; relTol 0.1 ; }; h smoothSolver { smoother GaussSeidel ; tolerance 1e-06 ; relTol 0.1 ; }; T smoothSolver { smoother GaussSeidel ; tolerance 1e-06 ; 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: 1,894 Rep Power: 26 Since the set-up works in other cases, I would check the mesh. P.S. It looks like you are using a non-standard version of simpleFOAM. best, __________________ Alberto Passalacqua 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. OpenQBMM - An open-source implementation of quadrature-based moment methods

 July 25, 2011, 02:56 #3 New Member   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 Senior Member   Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,894 Rep Power: 26 Good to hear it is working. Sometimes a few cells cause the problem, and the solution is not really affected ;-) __________________ Alberto Passalacqua 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. OpenQBMM - An open-source implementation of quadrature-based moment methods

 December 27, 2012, 16:07 #5 Senior Member   Join Date: Nov 2012 Posts: 168 Rep Power: 4 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 = 1.72098e-09, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000254413, Final residual = 2.84039e-09, No Iterations 1 GAMG: Solving for p, Initial residual = 0.140828, Final residual = 9.19848e-07, No Iterations 97 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors (Low Ma): sum local = 1.24031e-11, global = -8.09049e-14, cumulative = -6.05813e-11 rho max/min : 1.8221 1.1966 The setting for the pressure linear solver is as follows: "(p)" { solver GAMG; preconditioner FDIC; tolerance 1e-6; 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 hawkeye321 likes this.

 January 8, 2013, 17:38 #6 Member   ,... Join Date: Apr 2011 Posts: 92 Rep Power: 5 Hi hz283 Please let me know if you figures it out!

 March 5, 2013, 22:20 #7 Member   Nikesh Bhattarai Join Date: Nov 2011 Location: Daejeon, South Korea Posts: 70 Rep Power: 4 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 p-residuals are higher than the others Ux,Uy,k,omega, etc..

 Tags convergence issues, openfoam 1.6, simplefoam

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