[donree4]

Hey all,

This is my first post here, and i'm relatively new to OpenFOAM so forgive me for my inexperience and ignorance

I'm conducting a comparative study between ANSYS Fluent and OpenFOAM. I've simulated various turbulent annular flows in ANSYS Fluent and i'm now trying to replicate the results in OF (Identical mesh, turbulence model, numerical methods/procedures etc). The results show great agreement with experimental data for most cases, however one case has proven troublesome, and i'm not particularly sure as to why. Any support you guys can provide would be much appreciated

Potentially useful information:
The 'behaving' case (Nouri)
- External Radius: 40.3mm
- Internal Radius: 20.1mm (Radius ratio ~0.5)
- Reynolds Number: 8900
- Data type: Experimental

The 'troublesome' case (Chung)
- External Radius: 40.3mm
- Internal Radius: 4.03mm (Radius Ratio ~0.1)
- Reynolds Number: 8900
- Data type: DNS

Methods
- 2D asymmetric meshes were generated in ANSYS Fluent and converted to OpenFOAM using the 'FluentMeshToFoam' and 'makeAxialMesh' commands.
- Each case used identical case files, re-purposed (i.e with appropriate BCs) as appropriate. The code:

U

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1812 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volVectorField;
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //


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

internalField uniform (0 0 0);

boundaryField
{
inlet
{
type fixedValue;
value uniform (0.4 0 0);
}

topwall
{
type noSlip;
}

outlet
{
type zeroGradient;
}

bottomwall
{
type noSlip;
}

frontAndBackPlanes
{
type empty;
}

frontAndBackPlanes_pos
{
type wedge;
}

frontAndBackPlanes_neg
{
type wedge;
}

}
// ************************************************** *********************** //

P

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1812 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 0;

boundaryField
{
inlet
{
type zeroGradient;
}

topwall
{
type zeroGradient;
}

outlet
{
type fixedValue;
value uniform 0;
}

bottomwall
{
type zeroGradient;
}

frontAndBackPlanes
{
type empty;
}

frontAndBackPlanes_pos
{
type wedge;
}

frontAndBackPlanes_neg
{
type wedge;
}
}
// ************************************************** *********************** //

k

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1812 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object k;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 6e-4; // k =1.5 x (0.72 x 0.05)^2

boundaryField
{
inlet
{
type turbulentIntensityKineticEnergyInlet;
intensity 0.05;
value uniform 1;
}

outlet
{
type zeroGradient;
}

topwall
{
type fixedValue;
value uniform 1e-12;
}

bottomwall
{
type fixedValue;
value uniform 1e-12;
}

frontAndBackPlanes
{
type empty;
}

frontAndBackPlanes_pos
{
type wedge;
}

frontAndBackPlanes_neg
{
type wedge;
}
}

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

omega

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1812 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object omega;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 36.8098;

boundaryField
{
inlet
{
type fixedValue;
value 36.8098;
}

outlet
{
type zeroGradient;
}

topwall
{
type omegaWallFunction;
value $internalField;
}

bottomwall
{
type omegaWallFunction;
value $internalField;
}

frontAndBackPlanes
{
type empty;
}

frontAndBackPlanes_pos
{
type wedge;
}

frontAndBackPlanes_neg
{
type wedge;
}
}

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

nut

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1812 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
location "0";
object nut;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 0;

boundaryField
{
inlet
{
type calculated;
value uniform 0;
}

topwall
{
type nutkWallFunction;
value uniform 0;
}

outlet
{
type calculated;
value uniform 0;
}

bottomwall
{
type nutkWallFunction;
value uniform 0;
}

frontAndBackPlanes
{
type empty;
}

frontAndBackPlanes_pos
{
type wedge;
}

frontAndBackPlanes_neg
{
type wedge;
}
}

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

controlDict

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1812 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application simpleFoam;

startFrom latestTime;

stopAt endTime;

endTime 10000;

deltaT 1;

writeControl timeStep;

writeInterval 1;

purgeWrite 1;

writeFormat ascii;

writePrecision 10;

writeCompression off;

timeFormat general;

timePrecision 6;
// ************************************************** *********************** //

fvSchemes

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1812 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
ddtSchemes
{
default steadyState;
}

gradSchemes
{
default leastSquares;
}

divSchemes
{
default Gauss linear;
div(phi,U) Gauss linearUpwind grad(U);
div(phi,k) Gauss upwind;
div(phi,omega) Gauss upwind;
}

laplacianSchemes
{
default Gauss linear corrected;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default corrected;
}

wallDist
{
method meshWave;
}

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

fvSolution

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1812 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

U
{
solver GAMG;
smoother GaussSeidel;
tolerance 1e-06;
}

k
{
solver GAMG;
smoother GaussSeidel;
tolerance 1e-06;
}

omega
{
solver GAMG;
smoother GaussSeidel;
tolerance 1e-06;
}
}

SIMPLE
{
nNonOrthogonalCorrectors 0;
consistent no;

residualControl
{
p 1e-6;
U 1e-6;
k 1e-6;
omega 1e-6;
}
}

relaxationFactors
{
fields
{
p 0.3;
}
equations
{
U 0.7;
k 0.8;
omega 0.8;
}
}

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

turbulenceProperties

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1812 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "constant";
object turbulenceProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

simulationType RAS;

RAS
{
RASModel kOmegaSST;

turbulence on;

printCoeffs on;
}

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

transportProperties

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1812 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "constant";
object transportProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

nu 1.63e-6;

transportModel Newtonian;

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

Thanks in advance,
DonRee4

[donree4]

I found this related forum post (Problem with SST-Model - strange behaviour) that suggested reducing the k and omega tolerances from 1e-6 to 1e-12. I chose a value of 1e-10 instead for faster convergence and found that my results improved greatly (as seen in the attached). Hopefully this is useful to someone.