[cheng1]

Hello everyone, I am using SA model and simplefoam to solve the lift coefficient and drag coefficient of NACA0012. I adjusted many aspects, but I can't get the correct result. The lift coefficient obtained is 1.011, but the reference value is about 1.2. The drag coefficient is 0.037, and the reference value is around 0.012.
My nut is 1e-5 and nuTilda is 4e-5. If them are too small, case will crash. Re=6e+6, nu=1e-6, rho=1000, U=6, I can't get the correct result.
Does anyone know where my settings are going wrong?

FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application simpleFoam;

startFrom startTime;

startTime 0;

stopAt endTime;

endTime 0.24;

deltaT 0.0001;

writeControl timeStep;

writeInterval 100;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression off;

timeFormat general;

timePrecision 6;

runTimeModifiable true;

functions
{

forceCoeffs

{

type forceCoeffs;

functionObjectLibs ("libforces.so");

patches (FOIL);

log true;

rho rhoInf;

rhoInf 1000;

CofR (0 0 0);

liftDir (-0.17365 0.984808 0);

dragDir (0.984808 0.17365 0);

pitchAxis (0 0 1);

magUInf 6;

lRef 1;

Aref 0.3048; //This is the thickness of the grid in the Z direction.

writeControl adjustableRunTime;

writeInterval 0.1;

}

[cheng1]

FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object nuTilda;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 2 -1 0 0 0 0];

internalField uniform 4e-5;

boundaryField
{
INLET
{
type freestream;
freestreamValue uniform 4e-5;
}

OUTLET
{
type freestream;
freestreamValue uniform 4e-5;
}

FOIL
{
type fixedValue;
value uniform 0;
}

frontAndBackPlanes
{
type empty;
}
}


FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object nut;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 2 -1 0 0 0 0];

internalField uniform 1e-5;

boundaryField
{
INLET
{
type freestream;
freestreamValue uniform 1e-5;
}

OUTLET
{
type freestream;
freestreamValue uniform 1e-5;
}

FOIL
{
type nutUSpaldingWallFunction;
value uniform 0;
}

frontAndBackPlanes
{
type empty;
}


FoamFile
{
version 2.0;
format ascii;
class volVectorField;
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 1 -1 0 0 0 0];

internalField uniform (5.9088465 1.041889 0);

boundaryField
{
INLET
{
type freestreamVelocity;
freestreamValue $internalField;
}

OUTLET
{
type freestreamVelocity;
freestreamValue $internalField;
}

FOIL
{
type noSlip;
}

frontAndBackPlanes
{
type empty;
}
}


FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 2 -2 0 0 0 0];

internalField uniform 0;

boundaryField
{
INLET
{
type freestreamPressure;
freestreamValue $internalField;
}

OUTLET
{
type freestreamPressure;
freestreamValue $internalField;
}

FOIL
{
type zeroGradient;
}

frontAndBackPlanes
{
type empty;
}
}


FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
default steadyState;
}

gradSchemes
{
default Gauss linear;
}

divSchemes
{
default none;
div(phi,U) bounded Gauss linearUpwind grad(U);
div(phi,nuTilda) bounded Gauss linearUpwind grad(nuTilda);
div((nuEff*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
default Gauss linear corrected;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default corrected;
}

wallDist
{
method meshWave;
}


FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
p
{
solver GAMG;
tolerance 1e-06;
relTol 0.1;
smoother GaussSeidel;
}

U
{
solver smoothSolver;
smoother GaussSeidel;
nSweeps 2;
tolerance 1e-08;
relTol 0.1;
}

nuTilda
{
solver smoothSolver;
smoother GaussSeidel;
nSweeps 2;
tolerance 1e-08;
relTol 0.1;
}
}

SIMPLE
{
nNonOrthogonalCorrectors 0;

residualControl
{
p 1e-5;
U 1e-5;
nuTilda 1e-5;
}
}

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

[HPE]

Hi,

Would the following link help? https://www.cfd-online.com/Forums/op...tml#post800233

This issue seems to need a revisit.

Please let us know your feedback.

Thanks a lot.

[cheng1]

Originally Posted by HPE

Hi,

Would the following link help? https://www.cfd-online.com/Forums/op...tml#post800233

This issue seems to need a revisit.

Please let us know your feedback.

Thanks a lot.

Thank you, my mesh quality is too bad, now I can get the correct value.

[cheng1]

Originally Posted by HPE

Hi,

Would the following link help? https://www.cfd-online.com/Forums/op...tml#post800233

This issue seems to need a revisit.

Please let us know your feedback.

Thanks a lot.

Hello Hpe. I can get good results through your grid now. But now I need to use my own grid to get the results, but no matter how I modify my grid, I cannot get the correct drag coefficient Cd, which is always 20% to 30% larger than the experimental data. But a good lift coefficient can be obtained. Through the investigation of the problem, I found that the error appeared in the pressure drag, and there was no problem with the viscous drag. I still use the SA model, and y+ is strictly less than 1. Below is the result of my checkMesh.
If you want I can sent to you my project
Looking forward to your reply!





Create time

Create mesh for time = 0

Time = 0

Mesh stats
points: 298000
internal points: 0
faces: 594212
internal faces: 296212
cells: 148404
faces per cell: 6
boundary patches: 3
point zones: 0
face zones: 0
cell zones: 0

Overall number of cells of each type:
hexahedra: 148404
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 0
polyhedra: 0

Checking topology...
Boundary definition OK.
Cell to face addressing OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
Patch Faces Points Surface topology
airfoil 596 1192 ok (non-closed singly connected)
freestream 596 1192 ok (non-closed singly connected)
leftAndRight 296808 298000 ok (non-closed singly connected)

Checking faceZone topology for multiply connected surfaces...
No faceZones found.

Checking basic cellZone addressing...
No cellZones found.

Checking geometry...
Overall domain bounding box (-249.487 -249.992 -0.5) (250.425 249.992 0.5)
Mesh has 2 geometric (non-empty/wedge) directions (1 1 0)
Mesh has 2 solution (non-empty) directions (1 1 0)
All edges aligned with or perpendicular to non-empty directions.
Boundary openness (4.68794e-19 -7.21221e-20 3.01413e-19) OK.
Max cell openness = 1.74033e-15 OK.
Max aspect ratio = 72.8739 OK.
Minimum face area = 1.86956e-09. Maximum face area = 73.9388. Face area magnitudes OK.
Min volume = 1.86956e-09. Max volume = 73.9388. Total volume = 196252. Cell volumes OK.
Mesh non-orthogonality Max: 21.9774 average: 5.92132
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 0.23925 OK.
Coupled point location match (average 0) OK.

Mesh OK.

End