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Old   July 26, 2013, 00:18
Default PimpleFoam-Crashed
  #1
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Amin
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Hello

In order to simulate a laminar and incompressible flow past a cube i tried to use icoFoam, but the i did know how to stabilize this solver, because of the high courant number.

That is why i am trying to run the simulation now with pimpleFoam, but unlikely the solver is crashing too. I think because to time-step is very low...
Do you know how to stabilize icoFoam and how to fix the problem with pinmpleFoam?

It would be great if someone could help me solve the problem :

Here is the output of OF (simulation with pimpleFoam. OF 2.2.0):

Code:
Courant Number mean: 0.00905642 max: 10.7784
deltaT = 1.3457e-101
--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1029
    Increased the timePrecision from 261 to 262 to distinguish between timeNames at time 12.8518
Time = 12.851786558825548212325884378515183925628662109375

DILUPBiCG:  Solving for Ux, Initial residual = 0.425712, Final residual = 2.75527e-06, No Iterations 5
DILUPBiCG:  Solving for Uy, Initial residual = 0.285945, Final residual = 5.18152e-07, No Iterations 5
DICPCG:  Solving for p, Initial residual = 0.657594, Final residual = 0.014474, No Iterations 2
time step continuity errors : sum local = 4.37835e-05, global = -2.86105e-05, cumulative = -0.00487001
DICPCG:  Solving for p, Initial residual = 0.592278, Final residual = 8.3816e-07, No Iterations 163
time step continuity errors : sum local = 3.37411e-09, global = 6.57181e-11, cumulative = -0.00487001
ExecutionTime = 174.2 s  ClockTime = 201 s

Courant Number mean: 0.00538199 max: 5.49296
deltaT = 1.22493e-101
--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1029
    Increased the timePrecision from 262 to 263 to distinguish between timeNames at time 12.8518
Time = 12.851786558825548212325884378515183925628662109375

DILUPBiCG:  Solving for Ux, Initial residual = 0.319248, Final residual = 5.97266e-06, No Iterations 5
DILUPBiCG:  Solving for Uy, Initial residual = 0.284562, Final residual = 5.43627e-06, No Iterations 5
DICPCG:  Solving for p, Initial residual = 0.428836, Final residual = 0.0167637, No Iterations 2
time step continuity errors : sum local = 0.00011502, global = 6.84904e-05, cumulative = -0.00480151
DICPCG:  Solving for p, Initial residual = 0.306846, Final residual = 8.56454e-07, No Iterations 153
time step continuity errors : sum local = 1.01177e-08, global = 5.813e-11, cumulative = -0.00480151
ExecutionTime = 174.63 s  ClockTime = 201 s

Courant Number mean: 0.00810236 max: 7.03961
deltaT = 8.70027e-102
--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1029
    Increased the timePrecision from 263 to 264 to distinguish between timeNames at time 12.8518
Time = 12.851786558825548212325884378515183925628662109375

DILUPBiCG:  Solving for Ux, Initial residual = 0.456665, Final residual = 6.35141e-07, No Iterations 8
DILUPBiCG:  Solving for Uy, Initial residual = 0.375937, Final residual = 3.13479e-06, No Iterations 8
DICPCG:  Solving for p, Initial residual = 0.489683, Final residual = 0.0239404, No Iterations 26
time step continuity errors : sum local = 0.000190772, global = -4.11878e-05, cumulative = -0.0048427
DICPCG:  Solving for p, Initial residual = 0.449154, Final residual = 7.10247e-07, No Iterations 175
time step continuity errors : sum local = 1.31591e-08, global = -4.67166e-11, cumulative = -0.0048427
ExecutionTime = 175.14 s  ClockTime = 202 s

Courant Number mean: 0.0375239 max: 28.0087
deltaT = 1.55314e-102
--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1029
    Increased the timePrecision from 264 to 265 to distinguish between timeNames at time 12.8518
Time = 12.851786558825548212325884378515183925628662109375

#0  Foam::error::printStack(Foam::Ostream&) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"
#1  Foam::sigFpe::sigHandler(int) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"
#2   in "/lib/x86_64-linux-gnu/libc.so.6"
#3  double Foam::sumProd<double>(Foam::UList<double> const&, Foam::UList<double> const&) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"
#4  Foam::PBiCG::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"
#5  
 in "/opt/openfoam220/platforms/linux64GccDPOpt/bin/pimpleFoam"
#6  
 in "/opt/openfoam220/platforms/linux64GccDPOpt/bin/pimpleFoam"
#7  
 in "/opt/openfoam220/platforms/linux64GccDPOpt/bin/pimpleFoam"
#8  
 in "/opt/openfoam220/platforms/linux64GccDPOpt/bin/pimpleFoam"
#9  
 in "/opt/openfoam220/platforms/linux64GccDPOpt/bin/pimpleFoam"
#10  __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#11  
 in "/opt/openfoam220/platforms/linux64GccDPOpt/bin/pimpleFoam"
Floating point exception (core dumped)

Thx
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Old   July 26, 2013, 03:45
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Alexey Matveichev
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There are lots of reasons your solution is diverging (bad mesh, wrong IC, wrong BC etc). Can you please post you case files?
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Old   July 26, 2013, 03:50
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Amin
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please

http://www.workupload.com/file/h7RtY9U
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Old   July 26, 2013, 04:53
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Alexey Matveichev
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Well...

To make the case run it was enough to increase nNonOrthogonalCorrectors from 0 to 1.

But results are still rather strange so you can also increase nOuterCorrectors and nCorrectors. But better switch to residualControl for exit condition from PIMPLE loop.

This is just the correction of nNonOrthogonalCorrectors (fvSolution)
Code:
PIMPLE
{
    nOuterCorrectors 1;
    nCorrectors     2;
    nNonOrthogonalCorrectors 1;
    pRefCell        1001;
    pRefValue       0;
}
Velocity field is on velocity-field-1.png. You've switched off turbulence but still you get instabilities in the flow.

If we now switch on residualControl (fvSolution), reduce maxCo from 5 to 1 (in controlDict) and rerun the case we'll get results presented on velocity-field-2.png. And they seems to be more promising. Here's the fragment of fvSolution:
Code:
PIMPLE
{
    nOuterCorrectors 100;
    nCorrectors     3;
    nNonOrthogonalCorrectors 2;
    pRefCell        1001;
    pRefValue       0;

    residualControl
    {
        U
        {
            tolerance 1e-2;
            relTol 0;
        }

        p
        {
            tolerance 1e-2;
            relTol 0;
        }
    }
}
Also I've changed residuals for individual solvers:
Code:
    p
    {
        solver          PCG;
        preconditioner  DIC;
        tolerance       1e-06;
        relTol          1e-05;
    }

    pFinal
    {
        solver          PCG;
        preconditioner  DIC;
        tolerance       1e-08;
        relTol          0;
    }
Attached Images
File Type: png velocity-field-1.png (30.6 KB, 45 views)
File Type: png velocity-field-2.png (22.8 KB, 39 views)
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Old   July 26, 2013, 05:25
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Alexey Matveichev
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Was not exactly right about flow being laminar. Velocity field at 30 s is on attached file. But still flow has this "stable" von Carman vortex street
Attached Images
File Type: png velocity-field-3.png (61.2 KB, 33 views)
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