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Boundary conditions K-Omega SST. Air Knife Simulation

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Old   December 31, 2019, 04:18
Default Boundary conditions K-Omega SST. Air Knife Simulation
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Gustavo Barahona
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Hi everybody!

I'm analyzing several geometries for the construction of an Air Knife. I don't have much experience working with OpenFoam and my solution is not converging.


The speeds I am getting are extremely high (see attached image). After reading several Threads I realized that the error may be in the bcs.


In the actual application the total pressure at the inlet is about 300mbar. For p, U, k, w and nut files I used then this settings:

p File
internalField uniform 0;
boundaryField
{
fixedWalls
{
type zeroGradient;
}

//inlet
// {
// type zeroGradient;
// }

inlet
{
type totalPressure;
p0 uniform 3E4;
gamma 0.0;
value $internalField;
}
outlet
{
type fixedValue;
value uniform 0;
}
}


U File

boundaryField
{
fixedWalls
{
type noSlip;
}


inlet
{
type pressureInletVelocity;
value $internalField;
}

outlet
{
type zeroGradient;
}
}


k File
internalField uniform 2.34;
boundaryField
{
fixedWalls
{
type kqRWallFunction;
value uniform 0;
}

inlet
{
type turbulentIntensityKineticEnergyInlet;
intensity 0.05;
value $internalField;
}

outlet
{
type inletOutlet;
inletValue $internalField;
value $internalField;
}
}


omega File
internalField uniform 50;
boundaryField
{
inlet
{
type fixedValue;
value $internalField;
}

outlet
{
type inletOutlet;
inletValue $internalField;
value $internalField;
}

fixedWalls
{
type omegaWallFunction;
value $internalField;
}
}


nut File
internalField uniform 0;
boundaryField
{
inlet
{
type calculated;
value uniform 0;
}

outlet
{
type calculated;
value uniform 0;
}

fixedWalls
{
type nutkWallFunction;
value uniform 0;
}
}


From a previous simulation on a similar air knife, I calculated the k-value.

In that simulation the value of the velocity in the area of the Inlet was about 25 m/s. In a second simulation I tried to use this initial condition, but the simulation was always not converging.



p File
internalField uniform 0;
boundaryField
{
fixedWalls
{
type zeroGradient;
}

inlet
{
type zeroGradient;
}

outlet
{
type fixedValue;
value uniform 0;
}
}


U File
internalField uniform (0 0 0);
boundaryField
{
fixedWalls
{
type noSlip;
}

inlet
{
type fixedValue;
value uniform (25 0 0);
}

outlet
{
type zeroGradient;
}
}


My fvSchemes and fvSolutions:


solvers
{
p
{
solver GAMG;
smoother GaussSeidel;
tolerance 1e-7;
relTol 0.01;

}

Phi
{
$p;
}

U
{
solver smoothSolver;
smoother GaussSeidel;
tolerance 1e-8;
relTol 0.1;
nSweeps 1;
}

k
{
solver smoothSolver;
smoother GaussSeidel;
tolerance 1e-8;
relTol 0.1;
nSweeps 1;
}

omega
{
solver smoothSolver;
smoother GaussSeidel;
tolerance 1e-8;
relTol 0.1;
nSweeps 1;
}
}

SIMPLE
{
nNonOrthogonalCorrectors 0;
consistent yes;
residualControl
{
p 1e-3;
U 1e-3;
k 1e-3;
omega 1e-3;
}
}
potentialFlow
{
nNonOrthogonalCorrectors 10;
}
relaxationFactors
{
equations
{
U 0.9;
k 0.7;
omega 0.7;
}
}
cache
{
grad(U);
}


fvSchemes

ddtSchemes
{
default steadyState;
}

gradSchemes
{
default Gauss linear;
grad(U) cellLimited Gauss linear 1;
}

divSchemes
{
default none;
div(phi,U) bounded Gauss linearUpwindV grad(U);
div(phi,k) bounded Gauss upwind;
div(phi,omega) bounded Gauss upwind;
div((nuEff*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
default Gauss linear corrected;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default corrected;
}

wallDist
{
method meshWave;
}


The geometry has approximately 3 million cells. The checkMesh was also ok (see attached image).


Thank you very much for your time and I hope someone can help me with this problem.
Attached Images
File Type: png lsd02.png (49.7 KB, 16 views)
File Type: png checkMesh.png (74.8 KB, 11 views)
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