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-   -   Dealing with BC's in OF 1.6 (http://www.cfd-online.com/Forums/openfoam-solving/72286-dealing-bcs-1-6-a.html)

vkrastev February 1, 2010 10:17

Dealing with BC's in OF 1.6
 
1 Attachment(s)
Hello everybody,
I am an almost brand new OF user and I think I have some problems to set appropriate boundary conditons for a 2d incompressible aerodinamic case. The case in question is made up by a rectangular ambient simulating the wind tunnel, with inlet and outlet sections at the two sides. Immersed into the "tunnel" there is a 2d solid profile (initially I started simulating the flow around a very simple geometry, for instance a rectangular section). The inlet value of the velocity field has to be of about 4.28 m/s, and the Reynolds number referred to profile's lenght is of about 10^5. The solver I wish to use is the pisoFoam standard one for incompressible and unsteady flows, initially coupled with a k-epsilon standard RAS model. I tried to set the BC's and the other dictionaries (contrloDict, fvSchemes and fvSolution) having a look to the tutorials, but the results I have obtained are not good, because the velocity field seems more like a potential case one rather than a turbulent one, and also because the solution reaches convergence almost instantly. Down below I post the bc's, an image of the velocity field and the other dictionaries contents, so I will be quite happy if someone of us could tell me what I'm doing wrong...
Thank you in advance


controlDict dictionary:

application pisoFoam;

startFrom startTime;

startTime 0;

stopAt endTime;

endTime 0.1;

deltaT 1e-04;

writeControl runTime;

writeInterval 0.01;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression uncompressed;

timeFormat general;

timePrecision 6;

runTimeModifiable yes;


fvSchemes dictionary:

ddtSchemes
{
default Euler;
}

gradSchemes
{
default Gauss linear;
grad(p) Gauss linear;
grad(U) Gauss linear;
}

divSchemes
{
default none;
div(phi,U) Gauss upwind;
div(phi,k) Gauss upwind;
div(phi,epsilon) Gauss upwind;
div(phi,R) Gauss upwind;
div(R) Gauss linear;
div(phi,nuTilda) Gauss upwind;
div((nuEff*dev(grad(U).T()))) Gauss linear;
}

laplacianSchemes
{
default none;
laplacian(nuEff,U) Gauss linear corrected;
laplacian((1|A(U)),p) Gauss linear corrected;
laplacian(DkEff,k) Gauss linear corrected;
laplacian(DepsilonEff,epsilon) Gauss linear corrected;
laplacian(DREff,R) Gauss linear corrected;
laplacian(DnuTildaEff,nuTilda) Gauss linear corrected;
}

interpolationSchemes
{
default linear;
interpolate(U) linear;
}

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
p ;
}


fvSolution dictionary:

solvers
{
p
{
solver PCG;
preconditioner DIC;
tolerance 1e-06;
relTol 0.1;
}

pFinal
{
solver PCG;
preconditioner DIC;
tolerance 1e-06;
relTol 0;
}

U
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0;
}

UFinal
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0;
}

k
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0;
}

epsilon
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0;
}

R
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0;
}

nuTilda
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0;
}

}

PISO
{
nCorrectors 2;
nNonOrthogonalCorrectors 0;
}


BC's for the velocity field:

internalField uniform (0 0 0);

boundaryField
{
INLET
{
type fixedValue;
value uniform (4.28 0 0);
}

OUTLET
{
type zeroGradient;
}

SOLID WALLS
{
type fixedValue;
value uniform (0 0 0);
}


BC's for the kinematic pressure field:

internalField uniform 0;

boundaryField
{
INLET
{
type zeroGradient;
}

OUTLET
{
type fixedValue;
value uniform 0;
}

SOLID WALLS
{
type zeroGradient;
}


BC's for the TKE (k):

internalField uniform 0.0687;

boundaryField
{
INLET
{
type fixedValue;
value uniform 0.0687;
}
OUTLET
{
type zeroGradient;
}
SOLID WALLS
{
type kqRWallFunction;
Cmu 0.09;
kappa 0.41;
E 9.8;
value uniform 0.0687;
}


BC's for the TKE dissipation rate (epsilon):

internalField uniform 0.109;

boundaryField
{
INLET
{
type fixedValue;
value uniform 0.109;
}
OUTLET
{
type zeroGradient;
}
SOLID WALLS
{
type epsilonWallFunction;
Cmu 0.09;
kappa 0.41;
E 9.8;
value uniform 0.109;
}

BC's for the Reynolds stresses (R):

internalField uniform (0 0 0 0 0 0);

boundaryField
{
INLET
{
type fixedValue;
value uniform (0 0 0 0 0 0);
}

OUTLET
{
type zeroGradient;
}

SOLID WALLS
{
type kqRWallFunction;

}

BC's for the turbulent viscosity (nut):

internalField uniform 0;

boundaryField
{
INLET
{
type calculated;
value uniform 0;
}
OUTLET
{
type calculated;
value uniform 0;
}
SOLID WALLS
{
type nutWallFunction;
Cmu 0.09;
kappa 0.41;
E 9.8;
value uniform 0;
}

vkrastev February 2, 2010 07:13

Any suggestions?

panda60 February 2, 2010 07:32

Quote:

Originally Posted by vkrastev (Post 244567)
Any suggestions?


Do you have initilized your velocity field with potentialFoam ?
and the initial value of epsion could be larger , for example 100 times than the real value.
Good luck.

vkrastev February 2, 2010 08:52

Quote:

Originally Posted by panda60 (Post 244571)
Do you have initilized your velocity field with potentialFoam ?
and the initial value of epsion could be larger , for example 100 times than the real value.
Good luck.

1-No, I don't made any initialization of the velocity field. Is that always required for a transient simulation or it is simply a "good practice"?

2-I'll try to enlarge epsilon values and then I will post if there are some different results

Thanks

vkrastev February 2, 2010 09:07

No changes after enlarging epsilon by a 10^2 factor...:(

maalan September 4, 2012 11:58

vkrastev, did you finde how to solve your problem?? I am stucked with the same thing!!
Thank you in advance!


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