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High Courant numbre, icoFoam NACA4415

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Old   May 1, 2014, 10:34
Default High Courant numbre, icoFoam NACA4415
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Hello, I'm new in openFoam, I have to simulate a NACA4415 airfoil with icoFoam in Re200, for university work.

The airfoil is modeling like a rhombus whose vertex are joined to splines in blockmesh/edges. In paraFoam the geometry and the mesh look very good.

At the beginning the case is well simulated using a low dT (0.0001) because i am using a very concentrated mesh in the airfoil, and my Courant number is a bit little, but there is a moment in which it increases very fast, and the simulation fails.

Furthermore when I open paraFoam it is as the fluid doesn't flow well, it is very strange.

I have used checkMesh to verify the mesh and it says that it's ok...

If somebody can help me i will be very thankful because I don't know what to to do...

This is the error

Quote:
Time = 0.0032

Courant Number mean: 4.3884e+80 max: 2.20792e+83
DILUPBiCG: Solving for Ux, Initial residual = 0.999404, Final residual = 466.982, No Iterations 1001
DILUPBiCG: Solving for Uy, Initial residual = 0.998577, Final residual = 2.34745, No Iterations 1001
DICPCG: Solving for p, Initial residual = 1, Final residual = 1.81111, No Iterations 1001
time step continuity errors : sum local = 8.60401e+87, global = 7.06746e+83, cumulative = 7.0677e+83
DICPCG: Solving for p, Initial residual = 0.984747, Final residual = 37.8824, No Iterations 1001
time step continuity errors : sum local = 2.10408e+91, global = -3.49972e+89, cumulative = -3.49972e+89
ExecutionTime = 33.98 s ClockTime = 67 s

Time = 0.0033

Courant Number mean: 3.68725e+91 max: 3.77447e+94
DILUPBiCG: Solving for Ux, Initial residual = 0.999419, Final residual = 6.13094e+10, No Iterations 1001
DILUPBiCG: Solving for Uy, Initial residual = 0.997046, Final residual = 4.17694, No Iterations 1001
#0 Foam::error:rintStack(Foam::Ostream&) in "/opt/openfoam230/platforms/linuxGccDPOpt/lib/libOpenFOAM.so"
#1 Foam::sigFpe::sigHandler(int) in "/opt/openfoam230/platforms/linuxGccDPOpt/lib/libOpenFOAM.so"
#2 Uninterpreted:
#3 Foam::PCG::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const in "/opt/openfoam230/platforms/linuxGccDPOpt/lib/libOpenFOAM.so"
#4 Foam::fvMatrix<double>::solveSegregated(Foam::dict ionary const&) in "/opt/openfoam230/platforms/linuxGccDPOpt/lib/libfiniteVolume.so"
#5 Foam::fvMatrix<double>::solve(Foam::dictionary const&) in "/opt/openfoam230/platforms/linuxGccDPOpt/bin/icoFoam"
#6
in "/opt/openfoam230/platforms/linuxGccDPOpt/bin/icoFoam"
#7 __libc_start_main in "/lib/i386-linux-gnu/libc.so.6"
#8
in "/opt/openfoam230/platforms/linuxGccDPOpt/bin/icoFoam"
Excepci├│n de coma flotante (`core' generado)

A picture of my mesh




And my codes U, P and controlDict

U
Quote:
dimensions [0 1 -1 0 0 0 0];

internalField uniform (1 0 0);

boundaryField
{
Entrada
{
type fixedValue;
value uniform (1 0 0);
}

Salida
{
type zeroGradient;
}

ArribaAbajo
{
type zeroGradient;
}

Perfil
{
type fixedValue;
value uniform (0 0 0);
}

AlanteAtras
{
type empty;
}
}
P
Quote:
dimensions [0 2 -2 0 0 0 0];

internalField uniform 0;

boundaryField
{
Entrada
{
type fixedValue;
value uniform 1;
}

Salida
{
type fixedValue;
value uniform 0;
}

ArribaAbajo
{
type zeroGradient;
}

Perfil
{
type zeroGradient;
}

AlanteAtras
{
type empty;
}
}
controlDict
Quote:
application icoFoam;

startFrom startTime;

startTime 0;

stopAt endTime;

endTime 1;

deltaT 0.0001;

writeControl timeStep;

writeInterval 100;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression uncompressed;

timeFormat general;

timePrecision 6;

runTimeModifiable yes;


functions
{
forces
{
type forces;
functionObjectLibs ("libforces.so");
patches ("Perfil");
rhoName rhoInf;
rhoInf 1;
CofR (0.25 0.034375 0);
}

forceCoeffs
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
patches ("Perfil");
rhoName rhoInf;
rhoInf 1;
CofR (0.25 0.034375 0);
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0 1);
magUInf 1;
lRef 1;
Aref 0.1;
}
};
If you need more information please ask me.

Thanks!

Last edited by Unknox90; May 4, 2014 at 06:58.
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Old   June 26, 2014, 12:41
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  #2
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Joachim Herb
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You set the pressure to fixedValue on both, the inlet and the outlet. This will not work (in nearly all cases). Try setting the pressure to zeroGradient at the inlet.
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