[Lionel Ivan]

Hello Foamers,
I've experimenting converge problems with SimpleFoam, my intention is to run a Forced Heat Convection Case (FCTest), at first with a variation of tutorial's room "movingFanInRoom". As it had multiple problems, I re-wrote all the case in a new type of problem: a coil heat exchange tank. Schematically something like:

Tube Coil Heat Exchanger schematic - Image

With FreeCAD, I build some kind of version for my new case:

FCTest-3 Body Like - Image

Check Mesh give me:

/*---------------------------------------------------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
Build  : 7-1ff648926f77
Exec   : checkMesh
Date   : May 02 2020
Time   : 17:03:56
Host   : "3ece253b8250"
PID    : 366
I/O    : uncollated
Case   : /home/openfoam/run/FCTest-3
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster (fileModificationSkew 10)
allowSystemOperations : Allowing user-supplied system call operations

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create polyMesh for time = 0

Time = 0

Mesh stats
    points:           1793428
    faces:            4953396
    internal faces:   4722081
    cells:            1582927
    faces per cell:   6.1124
    boundary patches: 4
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     1499468
    prisms:        3566
    wedges:        0
    pyramids:      0
    tet wedges:    8
    tetrahedra:    0
    polyhedra:     79885
    Breakdown of polyhedra by number of faces:
        faces   number of cells
            4   6538
            5   7291
            6   7064
            9   51660
           12   6368
           15   964

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
                   inLet      248      287  ok (non-closed singly connected)
                  outLet      574      597  ok (non-closed singly connected)
              conteiner2   162660   162769  ok (non-closed singly connected)
                helice-3    67833    77515      ok (closed singly connected)

Checking geometry...
    Overall domain bounding box (0.00299734 0.00299863 0.00299783) (0.297003 0.200038 0.503003)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (-9.65822e-17 -6.47508e-16 5.6816e-16) OK.
    Max cell openness = 3.58514e-16 OK.
    Max aspect ratio = 10.7391 OK.
    Minimum face area = 2.77567e-07. Maximum face area = 2.19009e-05.  Face area magnitudes OK.
    Min volume = 6.26419e-10. Max volume = 5.67002e-08.  Total volume = 0.0277642.  Cell volumes OK.
    Mesh non-orthogonality Max: 64.9115 average: 8.08358
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 3.93848 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

End

My boundaries are 4, "Conteiner2" is the rectangular tank, "helice-3" is Coil, "inLet" the upper hole, and the "outLet" side hole. You can see a list here (image version).

Here's how case mesh looks like - image

When I run simpleFoam at first instance to check that flows goes fine, k grows up (blows up) from time 9 to 13 approximately when Foam experiments floating point exception. K max initially is around 2.27e0 but then jumps above 5e+68.

I analysed results with paraFoam and found a singularity point (see image1 or image2) where flows accelerates x2 approximately without a physical reason. Then the acceleration expands to all container like a bomb, and also K. I made a few cuts of that region (you can see image gallery).

I think that is a kind of mistake with wall calculations because I've got same singularity in my previous case (the room) also in a wall corner.

I'm investigating Convergent factors, but I'm really new in CFD and also OpenFoam, so probably there is something that I'm not seeing right now.

I change my relaxation factors (lower), and decrease my time step. It works better, i could reach T=14 but still having the same problem.


Here's my last fvSchemes and fvSolution code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.x                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p_rgh
    {
        solver           GAMG;
        tolerance        1e-7;   //antes -7
        relTol           0.01;

        smoother         DICGaussSeidel;

    }
  
    p
    {
        solver          GAMG;
        tolerance       1e-06;  //antes -6
        relTol          0.01;
        smoother        GaussSeidel;
    }

    "(U|k|epsilon|h)"
    {
        solver 		smoothSolver;
        smoother        symGaussSeidel;
        tolerance       1e-05; //antes -5
        relTol          0.01;
    }
}

SIMPLE
{
    nNonOrthogonalCorrectors 0;
    consistent      yes;

    residualControl
    {
        p               1e-2;
        U               1e-3;
        "(k|epsilon|omega|f|v2)" 1e-3;
    }
    pRefCell    0;
    pRefValue    0;
}

relaxationFactors
{
    equations
    {
        U               0.7; // 0.9 is more stable but 0.95 more convergent
	k		0.7;
	epsilon  	0.7;
        ".*"            0.7; // 0.9 is more stable but 0.95 more convergent
    }
}


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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.x                                   |
|   \\  /    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;
}

divSchemes
{
    default         none;
    div(phi,U)      bounded Gauss linearUpwind grad(U);
    div(phi,k)      bounded Gauss limitedLinear 1;
    div(phi,epsilon) bounded Gauss limitedLinear 1;
    div(phi,K)      bounded Gauss upwind;  
    div(phi,h)      bounded Gauss upwind; //limitedLinear 0.2
    // div(phi,omega)  bounded Gauss limitedLinear 1;
    // div(phi,v2)     bounded Gauss limitedLinear 1;
    div((nuEff*dev2(T(grad(U))))) Gauss linear;
    div(((rho*nuEff)*dev2(T(grad(U))))) Gauss linear;
    div(nonlinearStress) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

wallDist
{
    method meshWave;
}


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

I'm running OpenFoam 7 in Fedora Linux 31 inside a docker container, on a cuad-core Intel(R) Core(TM) i7-6500U CPU @ 2.50GHz with 8 GB of Ram and 5 GB of Swap.

All case files you can find in this link.
Error Log is here.

I'll appreciate all kind of help or advices,
Thanks you in advance