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-   -   Lift and drag coefficient with strange values for NACA airfoil (http://www.cfd-online.com/Forums/openfoam-solving/58081-lift-drag-coefficient-strange-values-naca-airfoil.html)

antonio_ing December 15, 2008 06:07

Hi everybody. I'm trying to
 
Hi everybody.

I'm trying to simulate the flow around a NACA airfoil with the simpleFoam solver using the Spalart Allmaras model with Re=1e6. Strangely, the boundary layer is very thick resembling flow separation. Also, the drag coefficient is 0.2 which, for an airfoil at 0 AOA, is quite high and the lift coefficient is 0.07 while xfoil gives me 0.5. I can understand that the drag should be higher using a turbulence model, but why the lift coeff is so low?.
I'm posting here all the files in the system directory just in case

--------------------------------------------------
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 1.5 |
| \ / A nd | Web: http://www.OpenFOAM.org |
| \/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application simpleFoam;

startFrom startTime;

startTime 4000;

stopAt endTime;

endTime 8000;

deltaT 1;

writeControl timeStep;

writeInterval 100;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression uncompressed;

timeFormat general;

timePrecision 6;

graphFormat raw;

runTimeModifiable yes;

functions
(
forces
{
type forces;
functionObjectLibs ("libforces.so"); //Lib to load -> dylib on Mac and so on Linux
patches (profile1 profile2);//Name of patche to integrate forces
rhoInf 1.0; //Reference density for fluid - can be changed later ...
CofR ( 0 0 0);
}
forceCoeffs
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
patches (profile1 profile2);
rhoInf 1.0;
CofR (0 0 0);
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0 0);
magUInf 100.0;
lRef 0.1;
Aref 0.01;
} );

// ************************************************** *********************** //

----------------------------------------------

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 1.5 |
| \ / A nd | Web: http://www.OpenFOAM.org |
| \/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
default steadyState;
}

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 limited 0.7;
laplacian(nu,U) Gauss linear limited 0.7;
laplacian((1|A(U)),p) Gauss linear limited 1;
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;
}

// ************************************************** *********************** //

-----------------------------------------------

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 1.5 |
| \ / A nd | Web: http://www.OpenFOAM.org |
| \/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
p PCG
{
preconditioner DIC;
tolerance 1e-08;
relTol 0;
};

U PBiCG
{
preconditioner DILU;
tolerance 1e-08;
relTol 0;
};
k PBiCG
{
preconditioner DILU;
tolerance 1e-08;
relTol 0.1;
};
epsilon PBiCG
{
preconditioner DILU;
tolerance 1e-08;
relTol 0.1;
};
R PBiCG
{
preconditioner DILU;
tolerance 1e-08;
relTol 0.1;
};
nuTilda PBiCG
{
preconditioner DILU;
tolerance 1e-08;
relTol 0.1;
};
}
/*
k BICCG 1e-06 0;
epsilon BICCG 1e-06 0;
R BICCG 1e-06 0;
nuTilda BICCG 1e-06 0;
*/
SIMPLE
{
nNonOrthogonalCorrectors 2;
}


PISO
{
nCorrectors 1;
nNonOrthogonalCorrectors 1;
/* pRefCell 0;
pRefValue 0;*/
}

relaxationFactors
{
p 0.3;
U 0.7;
k 0.5;
epsilon 0.5;
/* R 0.7;*/
nuTilda 0.7;
}

// ************************************************** *********************** //

antonio_ing December 15, 2008 09:21

I found the porblem. Close to
 
I found the porblem. Close to the Trailing edge the mesh was not so strong. I have increased there the number of cells there and now everything is better...!

lhcamilo December 16, 2008 04:51

what did you use to mesh it?
 
what did you use to mesh it?

antonio_ing December 17, 2008 08:00

gmsh. It is nice and powerful.
 
gmsh. It is nice and powerful. I wrote the mesh file through matlab and then compiled it with gmsh.

ivan_cozza December 19, 2008 04:49

Hi Antonio, did you use tet m
 
Hi Antonio,
did you use tet mesh, or a transfinite one?
How did you specifie the b.l. stretching?
I'm managing to use gmsh for airfoil meshing, but I have problems with wall resolving..

antonio_ing December 29, 2008 03:29

you are right ivan. Actually i
 
you are right ivan. Actually i have used the transfinite algorithm close to the profile surface and in the first part of the wake. With this method you can easily define the vertical or horizontal stretching of the cells close to the profile. The gmsh tutorials t3.geo and t6.geo helped me a lot in doing that

ivan_cozza December 29, 2008 10:17

Antonio, I tryed to do the sa
 
Antonio,
I tryed to do the same, and my guess was to use the tet meshing far from the foil in order to reduce the number of elements. Did you do something similar?
With which kind of results?

antonio_ing December 29, 2008 15:23

actualy I did the opposite sin
 
actualy I did the opposite since it is more important to have a cartesian grid close to the airfoil in order to simulate correctely the boundary layer evolution.

If you give me your mail I can send you some screenshots of my mesh or the code I have used in gmsh. Hopefully this will help you

naveen December 30, 2008 00:48

hi everyone i could not
 
hi everyone

i could not solve naca0012 case because my vertices are not working correctly...could u please send me naca 0012 vertices..

naveen January 20, 2009 03:52

hi everybody i am trying
 
hi everybody

i am trying to work on C type domain of naca 0012 airfoil case in openfoam 1.4.1,but i dont hav the vertices and edges for naca 0012 airfoil,can u please send me the vertices and edges for naca 0012 airfiol..

naveen January 20, 2009 04:22

hi everybody i am trying
 
hi everybody

i am trying to work on C type domain of naca 0012 airfoil case in openfoam 1.4.1,but i dont hav the vertices and edges for naca 0012 airfoil,can u please send me the vertices and edges for naca 0012 airfiol..

ivan_cozza January 20, 2009 04:38

Naveen, http://www.aerospac
 
Naveen,

http://www.aerospaceweb.org/question...ls/q0100.shtml

here you can find the naca 4 digit equation, but did you ever try to google "naca 0012"?

hjasak January 20, 2009 04:44

I have left the code, case and
 
I have left the code, case and results for you on:

http://powerlab.fsb.hr/ped/kturbo/Op...P/naca0012.tgz

It is unbelievable that all the work you did on this since December 2008 is to ask the same question over and over again. Which school did you go to?

Hrv

naveen January 20, 2009 04:49

hi yes i tried that webs
 
hi

yes i tried that website but i need the edges of naca 0012 airfoil to work in openfoam 1.4.1...can u send me the tutorial of naca 0012 airfoil in openfoam 1.4.1...including how to solve and postprocessing..

caw January 20, 2009 04:58

Dear Naveen, do you really ex
 
Dear Naveen,
do you really expect other people to do all the work for you?

Have a look here (google is your friend)

http://www.basiliscus.com/ProaSectio.../AppendixD.pdf

http://www.ppart.de/aerodynamics/profiles/NACA4.html

Christian

naveen January 20, 2009 05:03

hi thanks for replying..
 
hi

thanks for replying....

Rophys September 13, 2012 12:21

Hi all,

I'm doing some simulations using the OpenFoam 2.1 and I'd like to measure the following aerodynamic forces: Drag Coefficient, Lift Coefficient, Axial-force coefficient, Normal-force coefficient, Pitching-moment coefficient and center of pressure.

How can I state this in the controlDict ?

Many thanks.


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