[Vignesh Veeresparan]

Hello,

I'm a beginner to openFoam and currently trying to simulate rotation of fan using MRF approach. I have created a conformal mesh using Hypermesh.

I ran checkMesh and mesh looks pretty for me (If there are any issues, please let me know)

/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1906                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
Build  : v1906 OPENFOAM=1906
Arch   : "LSB;label=32;scalar=64"
Exec   : checkMesh
Date   : Feb 12 2020
Time   : 21:49:25
Host   : Vignesh-PC
PID    : 616
I/O    : uncollated
Case   : /mnt/d/simulation/fanFlow
nProcs : 1
trapFpe: Floating point exception trapping enabled (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster (fileModificationSkew 10)
allowSystemOperations : Allowing user-supplied system call operations

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

Create mesh for time = 0

Time = 0

Mesh stats
    points:           225514
    faces:            2588958
    internal faces:   2544430
    cells:            1283347
    faces per cell:   4
    boundary patches: 4
    point zones:      0
    face zones:       1
    cell zones:       3

Overall number of cells of each type:
    hexahedra:     0
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    1283347
    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
    inlet               1860     988      ok (non-closed singly connected)
    outlet              8518     4317     ok (non-closed singly connected)
    chamber             18292    9260     ok (non-closed singly connected)
    fan                 15858    7931     ok (closed singly connected)

Checking faceZone topology for multiply connected surfaces...
    FaceZone            Faces    Points   Surface topology
    Interior            2544430  225514   multiply connected (shared edge)
  <<Writing 224956 conflicting points to set nonManifoldPoints

Checking basic cellZone addressing...
    CellZone            Cells        Points       Volume       BoundingBox
    inletChamber        267858       50595        5.41539      (-1.919 -0.95 -0.75) (-0.0139995 0.95 0.75)
    outletChamber       609830       109539       4.26755      (-0.014 -0.95 -0.75) (1.486 0.95 0.75)
    mrfVolume           405659       77995        0.00724763   (-0.0140005 -0.1575 -0.1575) (0.0816005 0.1575 0.1575)

Checking geometry...
    Overall domain bounding box (-1.919 -0.95 -0.75) (1.486 0.95 0.75)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (-2.24949e-16 2.18239e-18 2.0636e-17) OK.
    Max cell openness = 2.929e-16 OK.
    Max aspect ratio = 11.6261 OK.
    Minimum face area = 9.76503e-08. Maximum face area = 0.00853048.  Face area magnitudes OK.
    Min volume = 1.68524e-11. Max volume = 0.000277516.  Total volume = 9.69019.  Cell volumes OK.
    Mesh non-orthogonality Max: 77.9451 average: 17.3283
   *Number of severely non-orthogonal (> 70 degrees) faces: 132.
    Non-orthogonality check OK.
  <<Writing 132 non-orthogonal faces to set nonOrthoFaces
    Face pyramids OK.
    Max skewness = 1.13764 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

When running simpleFoam it runs for very few iterations and stops writting log as below. I tried to debug on this issue and left helpless.

/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1906                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
Build  : v1906 OPENFOAM=1906
Arch   : "LSB;label=32;scalar=64"
Exec   : simpleFoam
Date   : Feb 12 2020
Time   : 21:44:13
Host   : Vignesh-PC
PID    : 615
I/O    : uncollated
Case   : /mnt/d/simulation/fanFlow
nProcs : 1
trapFpe: Floating point exception trapping enabled (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster (fileModificationSkew 10)
allowSystemOperations : Allowing user-supplied system call operations

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

Create mesh for time = 0


SIMPLE: convergence criteria
    field p      tolerance 1e-06
    field U      tolerance 1e-06
    field "(k|epsilon|omega|f|v2)"       tolerance 1e-06

Reading field p

Reading field U

Reading/calculating face flux field phi

Selecting incompressible transport model Newtonian
Selecting turbulence model type RAS
Selecting RAS turbulence model kEpsilon
RAS
{
    RASModel        kEpsilon;
    turbulence      on;
    printCoeffs     on;
    Cmu             0.09;
    C1              1.44;
    C2              1.92;
    C3              0;
    sigmak          1;
    sigmaEps        1.3;
}

Creating MRF zone list from MRFProperties
    creating MRF zone: MRF1
No finite volume options present

Starting time loop

Time = 1

smoothSolver:  Solving for Ux, Initial residual = 1, Final residual = 0.0648975, No Iterations 6
smoothSolver:  Solving for Uy, Initial residual = 1, Final residual = 0.0313598, No Iterations 4
smoothSolver:  Solving for Uz, Initial residual = 1, Final residual = 0.0318085, No Iterations 4
GAMG:  Solving for p, Initial residual = 1, Final residual = 0.0193307, No Iterations 10
GAMG:  Solving for p, Initial residual = 0.000915887, Final residual = 3.73558e-05, No Iterations 1
time step continuity errors : sum local = 4.08226, global = 0.0161181, cumulative = 0.0161181
smoothSolver:  Solving for epsilon, Initial residual = 0.396528, Final residual = 0.0324891, No Iterations 10
smoothSolver:  Solving for k, Initial residual = 0.99513, Final residual = 0.0848232, No Iterations 12
bounding k, min: -3.51945 max: 142226 average: 1808.5
ExecutionTime = 25.14 s  ClockTime = 25 s

Time = 2

smoothSolver:  Solving for Ux, Initial residual = 0.704528, Final residual = 0.0411686, No Iterations 2
smoothSolver:  Solving for Uy, Initial residual = 0.793176, Final residual = 0.0476032, No Iterations 2
smoothSolver:  Solving for Uz, Initial residual = 0.790307, Final residual = 0.0469006, No Iterations 2
GAMG:  Solving for p, Initial residual = 9.79768e-05, Final residual = 8.34731e-06, No Iterations 8
GAMG:  Solving for p, Initial residual = 2.25847e-07, Final residual = 2.25847e-07, No Iterations 0
time step continuity errors : sum local = 28.0243, global = -0.0184985, cumulative = -0.00238043
smoothSolver:  Solving for epsilon, Initial residual = 0.231206, Final residual = 0.0145491, No Iterations 4
bounding epsilon, min: -1.09915e+07 max: 1.32021e+10 average: 1.19479e+07
smoothSolver:  Solving for k, Initial residual = 0.801133, Final residual = 0.0460882, No Iterations 2
bounding k, min: -4.65838e+08 max: 1.32021e+10 average: 4.48082e+06
ExecutionTime = 41.01 s  ClockTime = 41 s

Time = 3

smoothSolver:  Solving for Ux, Initial residual = 0.527847, Final residual = 0.0329246, No Iterations 2
smoothSolver:  Solving for Uy, Initial residual = 0.336724, Final residual = 0.019906, No Iterations 2
smoothSolver:  Solving for Uz, Initial residual = 0.340194, Final residual = 0.018082, No Iterations 2
GAMG:  Solving for p, Initial residual = 4.6271e-06, Final residual = 4.6271e-06, No Iterations 0
GAMG:  Solving for p, Initial residual = 4.6271e-06, Final residual = 4.6271e-06, No Iterations 0
time step continuity errors : sum local = 331.646, global = 0.390038, cumulative = 0.387658
smoothSolver:  Solving for epsilon, Initial residual = 6.09212e-09, Final residual = 6.09212e-09, No Iterations 0
smoothSolver:  Solving for k, Initial residual = 4.68489e-10, Final residual = 4.68489e-10, No Iterations 0
ExecutionTime = 50.8 s  ClockTime = 51 s

Time = 4

smoothSolver:  Solving for Ux, Initial residual = 0.625306, Final residual = 0.0276635, No Iterations 2
smoothSolver:  Solving for Uy, Initial residual = 0.620408, Final residual = 0.0215387, No Iterations 2
smoothSolver:  Solving for Uz, Initial residual = 0.495431, Final residual = 0.0226165, No Iterations 2
GAMG:  Solving for p, Initial residual = 3.87494e-05, Final residual = 6.92502e-06, No Iterations 1
GAMG:  Solving for p, Initial residual = 0.00841698, Final residual = 0.000232902, No Iterations 3
time step continuity errors : sum local = 1.83448e+14, global = -6.03831e+12, cumulative = -6.03831e+12
smoothSolver:  Solving for epsilon, Initial residual = 0.00663023, Final residual = 0.000580367, No Iterations 6
bounding epsilon, min: -2.53324e+24 max: 7.65939e+28 average: 6.05538e+24
smoothSolver:  Solving for k, Initial residual = 2.62996e-15, Final residual = 2.62996e-15, No Iterations 0
ExecutionTime = 61.76 s  ClockTime = 62 s

Time = 5

smoothSolver:  Solving for Ux, Initial residual = 0.000354911, Final residual = 2.39284e-05, No Iterations 154
smoothSolver:  Solving for Uy, Initial residual = 0.00154294, Final residual = 0.000103431, No Iterations 144
smoothSolver:  Solving for Uz, Initial residual = 0.000252396, Final residual = 2.375e-05, No Iterations 156

It would be helpful if someone can point my mistake and provide solution.

Thanks in Advance!

Regards,
Vignesh

[NablaDyn]

You provide very limited Information. It is impossible to really pin down the problem. However, AFAIS, your mesh contains a lot of highly non-orthogobal faces, you are using a steady-state solver for a (transient?) MRF case. The residuals seem to behave weirdly. I assume you need to revise your whole setup.

[HPE]

Also, you may need to consider a turbulence model more numerically stable than kEpsilon, e.g. kOmegaSST, since epsilon seems to be the troublemaker up there.

No idea about BCs etc. I agree with NablaDyn that the setup may need further care.

[Vignesh Veeresparan]

Originally Posted by NablaDyn

You provide very limited Information. It is impossible to really pin down the problem. However, AFAIS, your mesh contains a lot of highly non-orthogobal faces, you are using a steady-state solver for a (transient?) MRF case. The residuals seem to behave weirdly. I assume you need to revise your whole setup.

Hello NablaDyn,

I would like to appreciate for your interest in this issue. First of all, I wanted to run steady state MRF Incompressible solver (I hope now with latest simpleFoam MRF is functional).

I have few questions as below

1. Do I need to share the entire simulation file to jolt down the issue?
2. I found few hundreds of non-orthogonal faces in my mesh. How do I fix it in openFoam or should I need to go back to meshing tool and try fixing mesh with no non-orthogonal mesh?
3. Residuals looks meeting the criteria with short interval.(Very Fast Convergence)
4. If I need to revise my setup, What do you think that I need to take care about?