[tommynego95]

Hi all,

I recently encountered a problem that i cannot overcome and i'd like to ask you expert CFD users some hints.
My k value is getting unbounded through the whole simulation and i suspect this fact is not letting the simulation converge and keeps residuals high.
Solver used for the simulation is simpleFoam and as turbulence model i'm using kOmegaSST.
Y+ values are averaging at 46.5 and the maximum value reached 486.
The mesh i'm using has been reported as image down below as the residuals.
In the residuals image we have:
Top-left: Residuals
Top-middle: pressure
Top-right: Velocities
Bottom-left: k
Bottom-middle: bounded quantities
Bottom-right: continuity equation errors

Pressure, velocities and k values are probed in the wake zone of the geometry

CheckMesh command gives the following:

Checking geometry...
Overall domain bounding box (-3 0 0) (9 3 1)
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 (-3.5492e-17 2.1743e-16 -6.57894e-14) OK.
Max cell openness = 1.9803e-16 OK.
Max aspect ratio = 4.00001 OK.
Minimum face area = 7.09312e-07. Maximum face area = 0.2. Face area magnitudes OK.
Min volume = 7.09312e-07. Max volume = 0.01. Total volume = 35.9615. Cell volumes OK.
Mesh non-orthogonality Max: 24.585 average: 2.81328
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 2.86834 OK.
Coupled point location match (average 0) OK.

Mesh OK.

What i tried to solve the problem:

• Setting gradient limiter to 1 for k value and using an upwind as discretization for the divergence term.
• Re-meshing domain refining elements on where i think vortices forms
• Lowered URF (under-relaxation factors) to favour convergence
• Tried to start the simulation with a potentialFoam solution and applied an applyBoundaryCondition with an -ybl of 0.003.
• Starting from a converged kEpsilon simulation

Here are my initial and boundary conditions:
U

/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 9
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
format ascii;
class volVectorField;
location "0";
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform (45 0 0);

boundaryField
{
inlet
{
type fixedValue;
value uniform (45 0 0);
}
outlet
{
type inletOutlet;
inletValue uniform (0 0 0);
value uniform (0 0 0);
}
top_symm
{
type slip;
value $internalField;
}
back_2d
{
type empty;
}
front_2d
{
type empty;
}
bot_symm
{
type symmetry;
}
wall_small
{
type fixedValue;
value uniform (0 0 0);
}
}


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

p

/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 9
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
format ascii;
class volScalarField;
location "0";
object p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 0;

boundaryField
{
inlet
{
type zeroGradient;
}
outlet
{
type fixedValue;
value uniform 0;
}
top_symm
{
//type zeroGradient;
type slip;
}
back_2d
{
type empty;
}
front_2d
{
type empty;
}
bot_symm
{
type symmetry;
}
wall_small
{
type zeroGradient;
}
}


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

k

/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 9
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
format ascii;
class volScalarField;
location "0";
object k;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

I 0.05;
internalField uniform 7.59375;

boundaryField
{
inlet
{
type turbulentIntensityKineticEnergyInlet;
intensity $I; //turbulent intensity
value $internalField;
}
outlet
{
type inletOutlet;
inletValue uniform 7.59375;
value uniform 7.59375;
}
top_symm
{/*
type kqRWallFunction;
value uniform 7.59375;*/
type slip;
}
back_2d
{
type empty;
}
front_2d
{
type empty;
}
bot_symm
{
type symmetry;
}
wall_small
{
type kqRWallFunction;
value uniform 7.59375;
}
}


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

omega

/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 9
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
format ascii;
class volScalarField;
location "0";
object omega;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

l 0.00005443310539518174;
internalField uniform 50625.00000000001;

boundaryField
{
inlet
{
type turbulentMixingLengthDissipationRateInlet;
mixingLength $l;
value $internalField;
}
outlet
{
type inletOutlet;
inletValue uniform 50625.00000000001;
value uniform 50625.00000000001;
}
top_symm
{/*
type omegaWallFunction;
value uniform 20736;*/
type slip;
}
back_2d
{
type empty;
}
front_2d
{
type empty;
}
bot_symm
{
type symmetry;
}
wall_small
{
type omegaWallFunction;
value uniform 20736;
}
}


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

nut

/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 9
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
format ascii;
class volScalarField;
location "0";
object nut;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

U 45;
I 0.05;
l 0.00005443310539518174;
visc #calc "1.224744871*($U*$I*$l)";
internalField uniform $visc;

boundaryField
{
inlet
{
type calculated;
value uniform $visc;
}
outlet
{
type calculated;
value uniform $visc;
}
top_symm
{/*
type nutkWallFunction;
value uniform 1e-10;*/
type slip;
}
back_2d
{
type empty;
}
front_2d
{
type empty;
}
bot_symm
{
type symmetry;
}
wall_small
{
type nutkWallFunction;
value uniform 1e-10;
}
}


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