
[Sponsors] 
January 27, 2013, 17:25 
pisoFoam  unstable pressure residual

#1 
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 49
Rep Power: 6 
I am looking to get some help figuring out why my pressure residual keeps rising. I am conducting an LES simulation; the mesh is pretty good quality (pure hexahedral), and mesh and boundary conditions are stable in FLUENT. But I need to implement this in OpenFOAM. Could someone take a look at my dictionaries and see if I am missing something? BTW I solved a steadystate using simpleFoam, which was fine, converged nicely.
I keep the Co number less than 0,5; even going as low as 0.05, but to no avail. U "/** C++ **\  =========    \\ / F ield  OpenFOAM: The Open Source CFD Toolbox   \\ / O peration  Version: 1.7.1   \\ / A nd  Web: www.OpenFOAM.com   \\/ M anipulation   \**/ FoamFile { version 2.0; format ascii; class volVectorField; object U; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 1 1 0 0 0 0]; internalField uniform (0 0 0); boundaryField { INLET { type fixedValue; value uniform (0.32 0 0); } OUTLET { type inletOutlet; inletValue uniform (0 0 0); value uniform (0 0 0); } WALLS { type fixedValue; value uniform (0 0 0); } LEAFLETSURFACE1 { type fixedValue; value uniform (0 0 0); } LEAFLETSURFACE2 { type fixedValue; value uniform (0 0 0); } BACKWALL { type fixedValue; value uniform (0 0 0); } } " p "/** C++ **\  =========    \\ / F ield  OpenFOAM: The Open Source CFD Toolbox   \\ / O peration  Version: 1.7.1   \\ / A nd  Web: www.OpenFOAM.com   \\/ M anipulation   \**/ FoamFile { version 2.0; format ascii; class volScalarField; object p; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 2 0 0 0 0]; internalField uniform 0; boundaryField { INLET { type zeroGradient; } OUTLET { type fixedValue; value uniform 0; } WALLS { type zeroGradient; } BACKWALL { type zeroGradient; } LEAFLETSURFACE1 { type zeroGradient; } LEAFLETSURFACE2 { type zeroGradient; } }" Really appreciate the help everyone. Cheers 

January 27, 2013, 17:30 
Update

#2 
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 49
Rep Power: 6 
Scheme, solution and control dictionaries
Schemes " solvers { p { solver GAMG; preconditioner DIC; agglomerator faceAreaPair; tolerance 1e05; relTol 0; nCellsInCoarsestLevel 25; mergeLevels 1; smoother GaussSeidel; nPreSweeps 0; nPostSweeps 2; nFinestSweeps 2; //maxIter 10; } pFinal { solver GAMG; preconditioner DIC; agglomerator faceAreaPair; tolerance 1e05; relTol 0; nCellsInCoarsestLevel 25; mergeLevels 1; smoother GaussSeidel; nPreSweeps 0; nPostSweeps 2; nFinestSweeps 2; //maxIter 10; } U { solver PBiCG; preconditioner DILU; tolerance 1e05; relTol 0; } k { solver PBiCG; preconditioner DILU; tolerance 1e05; relTol 0; } B { solver PBiCG; preconditioner DILU; tolerance 1e05; relTol 0; } nuTilda { solver PBiCG; preconditioner DILU; tolerance 1e05; relTol 0; } } PISO { nCorrectors 2; nNonOrthogonalCorrectors 10; } relaxationFactors { fields { p 0.3; } equations { U 0.7; k 0.7; B 0.7; nuTilda 0.7; } }" Solution " ddtSchemes { default backward; } gradSchemes { default Gauss linear; grad(p) Gauss linear; grad(U) Gauss linear; } divSchemes { default none; div(phi,U) Gauss linear; div(phi,k) Gauss linear; div(phi,B) Gauss linear; div(phi,nuTilda) Gauss linear; div(B) Gauss linear; div((nuEff*dev(T(grad(U))))) Gauss linear ; } laplacianSchemes { default none; laplacian(nuEff,U) Gauss linear corrected; laplacian((1A(U)),p) Gauss linear corrected; laplacian(DkEff,k) Gauss linear corrected; laplacian(DBEff,B) Gauss linear corrected; laplacian(DnuTildaEff,nuTilda) Gauss linear corrected; } interpolationSchemes { default linear; } snGradSchemes { default corrected; } fluxRequired { default no; p ; } " Control "application pisoFoam; startFrom startTime; startTime 0; stopAt endTime; endTime 1.8e03; deltaT 5e06; writeControl timeStep; writeInterval 100; purgeWrite 1; writeFormat ascii; writePrecision 6; writeCompression uncompressed; timeFormat general; timePrecision 6; runTimeModifiable yes; " 

January 27, 2013, 21:24 

#3  
Member
Eric Robertson
Join Date: Jul 2012
Posts: 95
Rep Power: 6 
I strongly suggest two things you should try, the most important one first and the latter one you don't have to but should.
First, change your div(phi,U) scheme to linear upwind. The syntax for this is below (this is in OpenFoam 2.0.0) Quote:
I have run a few submarine simulations using pisoFoam and LES. Both these things helped, but the scheme change helped the most by far. Can you also post a few iterations from your output file? 

January 28, 2013, 17:24 
Update

#4 
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 49
Rep Power: 6 
I have implemented that scheme. I will update you and let you know how it goes. DO you think upwinding this term will cause too much numerical dissipation?
Cheers: Adam 

January 28, 2013, 18:11 

#5 
Senior Member
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,209
Rep Power: 18 
dear msuaeronautics could you have a look to my schemes how to change to have a better schemes?
thanks a lot for your consideration. fvSchemes: Code:
ddtSchemes { default CrankNicholson 0.5; } gradSchemes { default Gauss linear; grad(p) Gauss linear; grad(U) faceLimited leastSquares 1.0; } divSchemes { default none; div(phi,U) Gauss linearUpwind grad(U); div(phid,p) Gauss limitedLinear 1; div(phi,K) Gauss upwind; div(phi,h) Gauss limitedLinear 1; div(phi,k) Gauss limitedLinear 1; div(phi,epsilon) Gauss limitedLinear 1; div(phi,R) Gauss limitedLinear 1; div(phi,omega) Gauss limitedLinear 1; div((rho*R)) Gauss upwind; div(R) Gauss upwind; div(U) Gauss upwind; div((muEff*dev2(T(grad(U))))) Gauss linear; div(tauMC) Gauss linear; } laplacianSchemes { default none; laplacian(muEff,U) Gauss linear uncorrected; laplacian(mut,U) Gauss linear uncorrected; laplacian(DkEff,k) Gauss linear uncorrected; laplacian(DepsilonEff,epsilon) Gauss linear uncorrected; laplacian(DREff,R) Gauss linear uncorrected; laplacian(DomegaEff,omega) Gauss linear uncorrected; laplacian((rho*(1A(U))),p) Gauss linear uncorrected; laplacian(alphaEff,h) Gauss linear uncorrected; laplacian(k,T) Gauss linear uncorrected; laplacian(alpha,e) Gauss linear uncorrected; laplacian(alphaEff,e) Gauss linear uncorrected; } interpolationSchemes { default linear; } snGradSchemes { default uncorrected; } fluxRequired { default no; p ; } Code:
solvers { p { /*solver PCG; preconditioner DIC; tolerance 1e12; relTol 0;*/ solver GAMG; smoother DICGaussSeidel; cacheAgglomeration true; nCellsInCoarsestLevel 500; nPreSweeps 0; nPostSweeps 2; nFinestSweeps 2; agglomerator faceAreaPair; mergeLevels 2; tolerance 1e012; relTol 0; } pFinal { $p; relTol 0; } "rho.*" { $p; tolerance 1e11; relTol 0; } "(UehRkepsilonomega)" { solver PBiCG; preconditioner DILU; tolerance 1e11; relTol 0; maxIter 25000; } "(UhRkepsilonomega)Final" { $U; relTol 0; } } PIMPLE { momentumPredictor yes; nOuterCorrectors 3; nCorrectors 3; nNonOrthogonalCorrectors 0; rhoMin rhoMin [ 1 3 0 0 0 ] 0.2; rhoMax rhoMax [ 1 3 0 0 0 ] 9; residualControl { "(Ukomega)" { relTol 0; tolerance 0.000000001; } } } 

January 28, 2013, 18:29 
Update

#6 
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 49
Rep Power: 6 
HI msu,
I tried implementing the new scheme as you suggested; however it looks like the solution is still unstable. I was flirting with Co = 0,5, so I am going to lower the timestep by an order of magnitude to see if that helps at all. I have a feeling it is my boundary conditions. I am use to (spoiled) CFX/FLUENT, so the software basically ensures the proper BCs are selected based on the simulation type. Would you mind looking over my text files? I feel I am close, since the mesh and case works in FLUENT. Cheers: Adam 

January 28, 2013, 18:31 
Update

#7 
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 49
Rep Power: 6 
BTW,
Here is my log file printout: /**\  =========    \\ / F ield  OpenFOAM: The Open Source CFD Toolbox   \\ / O peration  Version: 2.1.0   \\ / A nd  Web: www.OpenFOAM.org   \\/ M anipulation   \**/ Build : 2.1.00bc225064152 Exec : pisoFoam parallel Date : Jan 28 2013 Time : 16:54:10 Host : "adamdesktop" PID : 5905 Case : /home/adam/OpenFOAM/adam2.1.0/run/tutorials/incompressible/pisoFoam/hvles/ICEM_Mesh nProcs : 3 Slaves : 2 ( "adamdesktop.5906" "adamdesktop.5907" ) Pstream initialized with: floatTransfer : 0 nProcsSimpleSum : 0 commsType : nonBlocking sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE). fileModificationChecking : Monitoring runtime modified files using timeStampMaster allowSystemOperations : Disallowing usersupplied system call operations // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // Create time Create mesh for time = 0 Reading field p Reading field U Reading/calculating face flux field phi Selecting incompressible transport model Newtonian Selecting turbulence model type LESModel Selecting LES turbulence model Smagorinsky SmagorinskyCoeffs { filter simple; ce 1.048; ck 0.094; } Starting time loop Time = 5e06 Courant Number mean: 3.91885e06 max: 0.000809022 DILUPBiCG: Solving for Ux, Initial residual = 1, Final residual = 2.9278e07, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 1, Final residual = 5.79668e07, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 1, Final residual = 8.0736e07, No Iterations 1 GAMG: Solving for p, Initial residual = 1, Final residual = 9.84125e06, No Iterations 316 GAMG: Solving for p, Initial residual = 0.0239126, Final residual = 9.44877e06, No Iterations 57 GAMG: Solving for p, Initial residual = 0.00573113, Final residual = 9.31698e06, No Iterations 57 time step continuity errors : sum local = 2.6016e08, global = 5.32965e09, cumulative = 5.32965e09 GAMG: Solving for p, Initial residual = 0.0029541, Final residual = 9.352e06, No Iterations 37 GAMG: Solving for p, Initial residual = 0.00176045, Final residual = 9.55465e06, No Iterations 28 GAMG: Solving for p, Initial residual = 0.00113938, Final residual = 9.88603e06, No Iterations 18 time step continuity errors : sum local = 2.78767e08, global = 8.83835e09, cumulative = 3.5087e09 ExecutionTime = 330.97 s ClockTime = 334 s Time = 1e05 Courant Number mean: 0.00247512 max: 0.379089 DILUPBiCG: Solving for Ux, Initial residual = 0.896973, Final residual = 8.07473e09, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 0.329405, Final residual = 1.83947e09, No Iterations 2 DILUPBiCG: Solving for Uz, Initial residual = 0.338451, Final residual = 9.96146e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.0160771, Final residual = 9.34229e06, No Iterations 170 GAMG: Solving for p, Initial residual = 0.175421, Final residual = 9.36675e06, No Iterations 92 GAMG: Solving for p, Initial residual = 0.0523747, Final residual = 9.49166e06, No Iterations 95 time step continuity errors : sum local = 3.07509e09, global = 6.03653e10, cumulative = 4.11235e09 GAMG: Solving for p, Initial residual = 0.0273851, Final residual = 9.48644e06, No Iterations 69 GAMG: Solving for p, Initial residual = 0.0177397, Final residual = 9.47844e06, No Iterations 56 GAMG: Solving for p, Initial residual = 0.0119949, Final residual = 9.37767e06, No Iterations 38 time step continuity errors : sum local = 3.12546e09, global = 7.41131e10, cumulative = 4.85348e09 ExecutionTime = 671.41 s ClockTime = 679 s Time = 1.5e05 Courant Number mean: 0.00258897 max: 0.419215 DILUPBiCG: Solving for Ux, Initial residual = 0.344173, Final residual = 3.81834e06, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.0599225, Final residual = 1.77624e06, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.0811998, Final residual = 1.93254e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.0984746, Final residual = 9.80077e06, No Iterations 178 GAMG: Solving for p, Initial residual = 0.0589744, Final residual = 9.95854e06, No Iterations 51 GAMG: Solving for p, Initial residual = 0.0229215, Final residual = 9.65347e06, No Iterations 49 time step continuity errors : sum local = 2.05256e09, global = 3.96244e10, cumulative = 4.45724e09 GAMG: Solving for p, Initial residual = 0.0191667, Final residual = 8.85689e06, No Iterations 39 GAMG: Solving for p, Initial residual = 0.0177382, Final residual = 8.33729e06, No Iterations 21 GAMG: Solving for p, Initial residual = 0.0175461, Final residual = 9.41587e06, No Iterations 16 time step continuity errors : sum local = 2.01745e09, global = 3.88969e10, cumulative = 4.06827e09 ExecutionTime = 905.06 s ClockTime = 914 s Time = 2e05 Courant Number mean: 0.00263949 max: 0.437453 DILUPBiCG: Solving for Ux, Initial residual = 0.269823, Final residual = 3.86531e06, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.0335224, Final residual = 2.23216e06, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.0426193, Final residual = 1.84547e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.0671635, Final residual = 9.89268e06, No Iterations 132 GAMG: Solving for p, Initial residual = 0.0822601, Final residual = 9.68393e06, No Iterations 36 GAMG: Solving for p, Initial residual = 0.068387, Final residual = 8.89289e06, No Iterations 38 time step continuity errors : sum local = 9.64269e10, global = 1.54725e10, cumulative = 4.22299e09 GAMG: Solving for p, Initial residual = 0.0716998, Final residual = 9.40588e06, No Iterations 22 GAMG: Solving for p, Initial residual = 0.0748368, Final residual = 9.0256e06, No Iterations 26 GAMG: Solving for p, Initial residual = 0.0783009, Final residual = 9.37482e06, No Iterations 40 time step continuity errors : sum local = 1.02744e09, global = 3.10414e10, cumulative = 3.91258e09 ExecutionTime = 1103.4 s ClockTime = 1114 s Time = 2.5e05 Courant Number mean: 0.00264223 max: 0.439232 DILUPBiCG: Solving for Ux, Initial residual = 0.123124, Final residual = 4.64148e08, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 0.0245945, Final residual = 5.50988e06, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.029589, Final residual = 4.42106e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.179635, Final residual = 9.81425e06, No Iterations 144 GAMG: Solving for p, Initial residual = 0.243531, Final residual = 9.5501e06, No Iterations 61 GAMG: Solving for p, Initial residual = 0.250189, Final residual = 9.48497e06, No Iterations 64 time step continuity errors : sum local = 6.54896e10, global = 2.12459e10, cumulative = 4.12504e09 GAMG: Solving for p, Initial residual = 0.265897, Final residual = 8.92568e06, No Iterations 65 GAMG: Solving for p, Initial residual = 0.284315, Final residual = 9.40306e06, No Iterations 66 GAMG: Solving for p, Initial residual = 0.290986, Final residual = 9.02112e06, No Iterations 66 time step continuity errors : sum local = 6.71955e10, global = 2.06005e10, cumulative = 3.91903e09 ExecutionTime = 1398.48 s ClockTime = 1411 s Time = 3e05 Courant Number mean: 0.00263927 max: 0.433526 DILUPBiCG: Solving for Ux, Initial residual = 0.0538373, Final residual = 7.37212e08, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 0.0204126, Final residual = 1.1062e08, No Iterations 2 DILUPBiCG: Solving for Uz, Initial residual = 0.0188419, Final residual = 2.28729e08, No Iterations 2 GAMG: Solving for p, Initial residual = 0.472397, Final residual = 9.45574e06, No Iterations 122 GAMG: Solving for p, Initial residual = 0.546436, Final residual = 9.12948e06, No Iterations 79 GAMG: Solving for p, Initial residual = 0.585044, Final residual = 8.95127e06, No Iterations 85 time step continuity errors : sum local = 6.73667e10, global = 9.83321e11, cumulative = 3.8207e09 GAMG: Solving for p, Initial residual = 0.596208, Final residual = 9.6783e06, No Iterations 79 GAMG: Solving for p, Initial residual = 0.643603, Final residual = 9.04489e06, No Iterations 87 GAMG: Solving for p, Initial residual = 0.628462, Final residual = 9.57861e06, No Iterations 85 time step continuity errors : sum local = 8.8126e10, global = 1.12988e10, cumulative = 3.93369e09 ExecutionTime = 1733.64 s ClockTime = 1750 s Time = 3.5e05 Courant Number mean: 0.00264827 max: 0.795428 DILUPBiCG: Solving for Ux, Initial residual = 0.032021, Final residual = 7.87142e07, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 0.0351896, Final residual = 3.93019e07, No Iterations 2 DILUPBiCG: Solving for Uz, Initial residual = 0.025715, Final residual = 4.18695e07, No Iterations 2 GAMG: Solving for p, Initial residual = 0.797142, Final residual = 9.76751e06, No Iterations 85 GAMG: Solving for p, Initial residual = 0.779713, Final residual = 9.82709e06, No Iterations 91 GAMG: Solving for p, Initial residual = 0.83697, Final residual = 9.37075e06, No Iterations 91 time step continuity errors : sum local = 1.31314e09, global = 2.13586e10, cumulative = 3.7201e09 GAMG: Solving for p, Initial residual = 0.829189, Final residual = 9.62978e06, No Iterations 87 GAMG: Solving for p, Initial residual = 0.874832, Final residual = 8.79269e06, No Iterations 91 GAMG: Solving for p, Initial residual = 0.849942, Final residual = 9.68367e06, No Iterations 83 time step continuity errors : sum local = 1.90408e09, global = 4.02444e10, cumulative = 4.12255e09 ExecutionTime = 2076.11 s ClockTime = 2096 s Time = 4e05 Courant Number mean: 0.00270431 max: 2.20807 DILUPBiCG: Solving for Ux, Initial residual = 0.0464676, Final residual = 8.29943e06, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 0.0870791, Final residual = 9.52937e06, No Iterations 2 DILUPBiCG: Solving for Uz, Initial residual = 0.0609628, Final residual = 2.05242e07, No Iterations 3 ^Cmpirun: killing job... 

January 28, 2013, 19:29 

#8  
Member
Eric Robertson
Join Date: Jul 2012
Posts: 95
Rep Power: 6 
Quote:
Might I ask about this parameter in your fvSolution file? Quote:
Quote:


January 28, 2013, 19:31 
Reply

#9 
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 49
Rep Power: 6 
I reduced those to 2, but it didn't improve the situation. I also reduced the timestep, and it didn't help either. Might I send you my boundary dictionaries? Ithink I may have accidentally set a boundary value incorrectly...but I don't see it. Although, as I mentioned, I usually use commercial solvers.
Cheers: Adam 

January 28, 2013, 19:57 

#10  
Member
Eric Robertson
Join Date: Jul 2012
Posts: 95
Rep Power: 6 
Quote:
I also wonder if GAMG for pressure has anything to do with this, though I can't say for sure. 

January 28, 2013, 20:27 
Dictionaries

#11 
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 49
Rep Power: 6 
'B'
FoamFile { version 2.0; format ascii; class volTensorField; object B; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 2 0 0 0 0]; internalField uniform (0 0 0 0 0 0 0 0 0); boundaryField { INLET { type fixedValue; value uniform (0 0 0 0 0 0 0 0 0); } OUTLET { type inletOutlet; inletValue uniform (0 0 0 0 0 0 0 0 0); value uniform (0 0 0 0 0 0 0 0 0); } WALLS { type zeroGradient; } LEAFLETSURFACE1 { type zeroGradient; } LEAFLETSURFACE2 { type zeroGradient; } BACKWALL { type zeroGradient; } } 'k' dimensions [0 2 2 0 0 0 0]; internalField uniform 1e10; boundaryField { INLET { type fixedValue; value uniform 1e10; } OUTLET { type inletOutlet; inletValue uniform 1e10; value uniform 1e10; } WALLS { type fixedValue; value uniform 1e10; } BACKWALL { type fixedValue; value uniform 1e10; } LEAFLETSURFACE1 { type fixedValue; value uniform 1e10; } LEAFLETSURFACE2 { type fixedValue; value uniform 1e10; } } // ************************************************** *********************** // 'nusgs' * // dimensions [0 2 1 0 0 0 0]; internalField uniform 0; boundaryField { INLET { type zeroGradient; } OUTLET { type zeroGradient; } WALLS { type zeroGradient; } LEAFLETSURFACE1 { type zeroGradient; } LEAFLETSURFACE2 { type zeroGradient; } BACKWALL { type zeroGradient; } } // ********* 'nutilda' dimensions [0 2 1 0 0 0 0]; internalField uniform 0; boundaryField { INLET { type fixedValue; value uniform 0; } OUTLET { type inletOutlet; inletValue uniform 0; value uniform 0; } WALLS { type fixedValue; value uniform 0; } LEAFLETSURFACE1 { type fixedValue; value uniform 0; } LEAFLETSURFACE2 { type fixedValue; value uniform 0; } BACKWALL { type fixedValue; value uniform 0; } } // 'p' dimensions [0 2 2 0 0 0 0]; internalField uniform 0; boundaryField { INLET { type zeroGradient; } OUTLET { type fixedValue; value uniform 0; } WALLS { type zeroGradient; } BACKWALL { type zeroGradient; } LEAFLETSURFACE1 { type zeroGradient; } LEAFLETSURFACE2 { type zeroGradient; } } 'U' dimensions [0 1 1 0 0 0 0]; internalField uniform (0 0 0); boundaryField { INLET { type fixedValue; value uniform (0.32 0 0); } OUTLET { type outletInlet; inletValue uniform (0 0 0); value uniform (0 0 0); } WALLS { type fixedValue; value uniform (0 0 0); } LEAFLETSURFACE1 { type fixedValue; value uniform (0 0 0); } LEAFLETSURFACE2 { type fixedValue; value uniform (0 0 0); } BACKWALL { type fixedValue; value uniform (0 0 0); } } // ************ Thanks a lot for taking a look. I am really perplexed... Cheers: Adam 

January 29, 2013, 07:19 

#12 
Senior Member
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,209
Rep Power: 18 
I want to improve stability.my problem is unsteady compressible with rhoPimpleFoam or rhoCentralFoam.my geometry is simple with rectangular cells and BC's are varying with time.I'm simulating Wave Rotor if you have ever heard about it.
thanks. 

January 29, 2013, 14:00 
Update

#13 
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 49
Rep Power: 6 
I am starting to wonder if my mesh was somehow improperly converted from a fluent3d mesh to an openfoam mesh. I can't find any problems with my boundary conditions, and if I use the same mesh in FLUENT it converges with no problem, even with a pretty similar setup.
FLUENT settings: PISO solver, 1 skewness correction Gradient Schemes: Gauss cell based Pressure Scheme: Second order Momentum Scheme: Central Differencing Transient: Second order implicit AMG solver settings Smoother> GaussSeidel 0 pre sweeps 1 post sweep Standard Limiter (cell to face) 

January 29, 2013, 22:42 

#14 
Member
Eric Robertson
Join Date: Jul 2012
Posts: 95
Rep Power: 6 
With regards to your BC's, I'm wondering about the outletInlet condition. If I remember correctly, changing from an inletOutlet for my inlet U to just a fixedValue helped my LES sim.
Otherwise, you probably do have to consider the mesh, as you suggested. I suppose you ran checkMesh in OpenFOAM already? 

January 30, 2013, 05:45 

#15 
Senior Member
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,209
Rep Power: 18 
dear msuaeronautics
Could you please have a look into my schemes and say what other changes are better to done for more stability? As i told my case is unsteady,compressible with rhoCentralFoam.im looking forward to your answer.also could you send me your fvScheme and fvSolution? Do you know anything about residualControl in rhoPimpleFoam and its duty? Thank you. 

January 30, 2013, 10:46 
Reply

#16 
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 49
Rep Power: 6 
Msu,
Thank's for the advice. I will try that. The checkMesh shows some highly skewed cells, but the ICEM output doesn't. The min Orthagonal quality (in ICEM is 0.3), and the min Skew (in ICEM is 0.25), which is a very good mesh. But OpenFOAM is giving me errors about highly skewed cells. Immortality, It looks like you have a lot of upwinding, and limiters in your scheme; this should produce stable results. Do a checkMesh. Also post your BCs. Cheers 

January 31, 2013, 21:54 
Still no luck

#17 
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 49
Rep Power: 6 
FLUENT converges completely fine, but OpenFOAM blows up. Completely lost on what BC to implement....Anyone out there have any suggestions?


February 2, 2013, 12:23 

#18 
Member
Eric Robertson
Join Date: Jul 2012
Posts: 95
Rep Power: 6 
Did you ever try switching from GAMG?


February 2, 2013, 13:25 
Reply

#19 
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 49
Rep Power: 6 
I currently still have GAMG, but I switched to pimplefoam which added some stability. The 'outflow' BC in fluent works brilliantly. That's the only difference I see, so I am trying to fix my outlet BC.
I am currently trying to compile fixedMeanValue, which should be more stable, the compilation isn't working though. 

February 21, 2013, 12:32 

#20 
Senior Member
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,209
Rep Power: 18 
did you compile that?can you send me the fixedMeanValue folder?


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Moving mesh  Niklas Wikstrom (Wikstrom)  OpenFOAM Running, Solving & CFD  122  June 15, 2014 06:20 
Floating point exception error  Alan  OpenFOAM Running, Solving & CFD  10  April 6, 2012 14:02 
High Courant Number @ icoFoam  Artex85  OpenFOAM Running, Solving & CFD  9  January 3, 2012 09:06 
Low Mach number Compressible jet flow using LES  ankgupta8um  OpenFOAM Running, Solving & CFD  7  January 15, 2011 14:38 
Unknown error  sivakumar  OpenFOAM PreProcessing  9  September 9, 2008 12:53 