2nd Order Schemes


#1

I have solved a case with satisfactory convergence ,that includes an fsae car using the recommended schemes in the numerics tab.But i noticed that these are mainly 1st order schemes in the divergence discretisation.Simultaneously I have solved the same case using OpenFOAM with 2nd orded schmes and noticed a 22% difference in force coeffs which is significant.Now I am trying to solve the same case in SimScale with 2nd order schemes but seems that I have done something wrong because of the fact that the case did not converge.I am attaching images with the convergence plot and the numerics settings of the case both with the 1st order schemes and the 2nd order that I used.

Thank you for your time!

1st order schemes:

Convergence plot of 1st order schemes

2nd order schemes:

Convergence plot of 2nd order schemes


#2

Hi @kkotsarinis and thanks for your question(s)!

Do you mind sharing your project link with us in the comment section? Makes it easier for us to see what settings you have chosen for your model, how the mesh looks like etc. - the @PowerUsers_CFD and I will have a look at your project then and get back to you as soon as we have found a solution to this problem.

Cheers and thanks!

Jousef


#3

This is the link of the simulation: https://www.simscale.com/workbench/?pid=3405221848583193277#tab_0-0


#4

@kkotsarinis, I also think it would be beneficial if you share your setup for your OpenFOAM run also, I presume the SimScale setup is identical to your OpenFOAM setup?

Kind regards,
Darren


#5

Here are the files of the OpenFOAM case:

fvSchemes:

/--------------------------------- C++ -----------------------------------
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 1.6 |
| \ / A nd | Web: www.OpenFOAM.org |
| \/ M anipulation | |
*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location “system”;
object fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
default steadyState;
}

gradSchemes
{
default Gauss linear;
grad§ Gauss linear;
grad(U) cellLimited Gauss linear 1;
// gradU cellLimited Gauss linear 1;
// grad(nuTilda) cellLimited Gauss linear 1;
// gradNuTilda cellLimited Gauss linear 1;
}

divSchemes
{
default Gauss linear;
div(phi,U) bounded Gauss linearUpwind gradU;
div(phi,nuTilda) bounded Gauss linearUpwind gradU;
//div(phi,nuTilda) bounded Gauss upwind;
div((nuEff*dev(grad(U).T()))) Gauss linear;
}

laplacianSchemes
{
default Gauss linear corrected; // Gauss linear limited corrected 0.33;
}

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

snGradSchemes
{
default corrected; //limited corrected 0.33;
}

fluxRequired
{
default no;
p ;
Phi ;
}

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

fvSolution:

/--------------------------------- C++ -----------------------------------
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 2.4.0 |
| \ / A nd | Web: www.OpenFOAM.org |
| \/ M anipulation | |
*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
“§”
{
solver GAMG;
agglomerator faceAreaPair;
mergeLevels 1;
cacheAgglomeration on;
nCellsInCoarsestLevel 200;
tolerance 1e-11;
relTol 0.01;
smoother GaussSeidel;
nPreSweeps 0;
nPostSweeps 2;
nFinestSweeps 2;
minIter 1;
}

"(U|nuTilda)"
{
    solver          PBiCG;
preconditioner  DILU;
tolerance 	1e-15;
relTol		0.01;
}

// Phi
// {
// $p;
// }
}

SIMPLE
{
nNonOrthogonalCorrectors 0;
}

potentialFlow
{
nNonOrthogonalCorrectors 10;
}

relaxationFactors
{
fields
{
p 0.2;
}
equations
{
U 0.5;
nuTilda 0.5;
}
}

cache
{
grad(U);
}

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


#6

Yes, I am trying to make an idetical setup and compare the results.


#9

@kkotsarinis, Could you also show me your turbulenceProperties?

Cheers,
Darren


#10

@1318980 these are the files
turbulence properties:

/--------------------------------- C++ -----------------------------------
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 2.1.x |
| \ / A nd | Web: www.OpenFOAM.org |
| \/ M anipulation | |
*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object turbulenceProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

simulationType RASModel;

// ************************************************************************* //
transport properties:
/--------------------------------- C++ -----------------------------------
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 2.4.0 |
| \ / A nd | Web: www.OpenFOAM.org |
| \/ M anipulation | |
*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object transportProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

transportModel Newtonian;

nu nu [0 2 -1 0 0 0 0] 1.511e-05;

// ************************************************************************* //
RASProperties:
/--------------------------------- C++ -----------------------------------
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 2.4.0 |
| \ / A nd | Web: www.OpenFOAM.org |
| \/ M anipulation | |
*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object RASProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

RASModel kOmegaSST;

turbulence on;

printCoeffs on;

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