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Setting U fixed value at the outlet?

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Old   April 23, 2015, 08:02
Default Setting U fixed value at the outlet?
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Hello,

I am testing a very simple 3D cylinder case with OF v2.3.0 however I get some strange results and thought I could ask here.

As mentioned, the model is a 3D cylinder surface-meshed with Tria elements and the volume mesh consists of Penta-element boundary layers and Tetra elements for the rest of the domain.

Instead of applying the proper BCs at the inlet (U fixed value, p zeroGradient) and outlet (U inletOutlet, p fixedValue 0) I use the following:

inlet:
p fixed value 0
U outletInlet
k outletInlet
omega outletInlet

outlet:
p zeroGradient
U fixed value 5
k inletOutlet
omega inletOutlet

In other words I try to impose a constant velocity at the outlet coming out of the domain.

However the results are not quite as expected. As shown in the pictures below, velocity gets too high at the inlet and propagates to the rest of the domain as iterations increase.

https://www.dropbox.com/s/mi70oucltvtf6a3/1.JPG?dl=0

https://www.dropbox.com/s/nf3ptm9lghuufu0/2.JPG?dl=0

https://www.dropbox.com/s/vijpkoov3xk7901/3.JPG?dl=0

Also, velocity is not uniform (5 m/s) at the outlet as set.

Turbulence model: k-omega SST
solver: simpleFoam
OF version: 2.3.0

Here is the fvSchemes file:
Quote:
ddtSchemes
{
default steadyState;
}

gradSchemes
{
default Gauss linear;
// grad(U) cellLimited Gauss linear 1;
// grad(nuTilda) 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(phi,nuTilda) bounded Gauss upwind;
div((nuEff*dev(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
default Gauss linear corrected;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
p;
}
Here is the fvSolution file:
Quote:
solvers
{
p
{
solver GAMG;
tolerance 1e-10;
relTol 0.05;
smoother GaussSeidel;
nPreSweeps 0;
nPostSweeps 2;
cacheAgglomeration on;
agglomerator faceAreaPair;
nCellsInCoarsestLevel 10;
mergeLevels 1;
}

U
{
solver smoothSolver;
smoother GaussSeidel;
tolerance 1e-10;
relTol 0.1;
nSweeps 1;
}

"(k|epsilon|omega|nuTilda)"
{
solver smoothSolver;
smoother GaussSeidel;
tolerance 1e-10;
relTol 0.1;
nSweeps 1;
}
}

SIMPLE
{
nNonOrthogonalCorrectors 0;

residualControl
{
p 1e-4;
U 1e-3;
k 1e-3;
omega 1e-3;
nuTilda 1e-3;
}
}

potentialFlow
{
nNonOrthogonalCorrectors 5;
}

relaxationFactors
{
fields
{
p 0.3;
}
equations
{
U 0.7;
k 0.7;
omega 0.7;
nuTilda 0.7;
}
}

cache
{
grad(U);
}
Here is the the trasportProperties file:
Quote:
transportModel Newtonian;

nu nu [0 2 -1 0 0 0 0] 1.51129E-005;
It seems like it is something related to the BCs definition.

Any ideas would be very helpful.

Thanks a lot in advance,
Greg
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