[calim_cfd]

Hello FoaMMers!

recently i've bumped into a large case.

Here's my mesh

Create time

Create polyMesh for time = 0

Time = 0

Mesh stats
    points:           1015757
    faces:            9905831
    internal faces:   9525541
    cells:            4779375
    boundary patches: 6
    point zones:      0
    face zones:       1
    cell zones:       1

Overall number of cells of each type:
    hexahedra:     64800
    prisms:        180792
    wedges:        0
    pyramids:      3480
    tet wedges:    0
    tetrahedra:    4530303
    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               1080     1147     ok (non-closed singly connected)  
    outlet              1080     1147     ok (non-closed singly connected)  
    wall_slip           5610     5762     ok (non-closed singly connected)  
    wall_fix            175509   89105    ok (non-closed singly connected)  
    wall_rot            180792   90405    ok (non-closed singly connected)  
    symmetry            16219    9357     ok (non-closed singly connected)  

Checking geometry...
    Overall domain bounding box (-2.27374e-16 -3.16552e-05 -0.300001) (12 4 4.5)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (5.37104e-19 3.74601e-18 -1.04857e-19) OK.
    Max cell openness = 2.20757e-16 OK.
    Max aspect ratio = 7.16421 OK.
    Minumum face area = 1.02019e-06. Maximum face area = 0.218717.  Face area magnitudes OK.
    Min volume = 5.87175e-10. Max volume = 0.0654096.  Total volume = 228.604.  Cell volumes OK.
    Mesh non-orthogonality Max: 66.0138 average: 14.7843
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 2.28739 OK.

Mesh OK.

End

schemes and solver are, respectively:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.0.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default         steadyState;
}

gradSchemes
{
    default         Gauss linear;
}

divSchemes
{
    default         none;
    div(phi,U)      Gauss linearUpwindV grad(U);
    div(phi,k)      Gauss upwind;
    div(phi,omega)  Gauss upwind;
    div((nuEff*dev(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear limited 0.333;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         limited 0.333;
}

fluxRequired
{
    default         no;
    p;
}

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

solvers
{
    p
    {
        solver           GAMG;
        tolerance        1e-7;
        relTol           0.001;
        smoother         GaussSeidel;
        nPreSweeps       0;
        nPostSweeps      2;
        cacheAgglomeration on;
        agglomerator     faceAreaPair;
        nCellsInCoarsestLevel 10;
        mergeLevels      1;
    }

    U
    {
        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-8;
        relTol           0.0001;
        nSweeps          1;
    }

    k
    {
        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-8;
        relTol           0.001;
        nSweeps          1;
    }

    omega
    {
        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-8;
        relTol           0.001;
        nSweeps          1;
    }
}

SIMPLE
{
    nNonOrthogonalCorrectors 2;
    
    residualControl
     {
        p               1e-6;
        U               1e-6;
        "(k|omega)"   1e-6;
    }
    
}

potentialFlow
{
    nNonOrthogonalCorrectors 10;
}

relaxationFactors
{
    p               0.3;
    U               0.7;
    k               0.7;
    omega           0.7;
}

cache
{
    grad(U);
}

These are the last ~100 iterations of a bunch with 9600



edit: can any of you check those settings and c if there's sth weird?? that's a too slow convergence rate....that residual pattern had already been established over 8000 iterations behind (posted a larger history with EDIT).. i'm just wondering whether i messed up the settings and this could be improved/speed up..or is this just a mesh size issue?

im running simpleFoam on 4 core with scotch,
i dont think my bc should be a problem... this is my domain..

here are some mesh closes




im not aiming at E-6 residuals, even thou that's what i wanted, but sth better than 0.02!

many many thanks!

[olivierG]

hello,

Just some hint ...
- Since it's steady state, you may take a look at local time stepping.
- use hex / polyhedre instead of tet mesh

regards,
olivier

[caramelo]

What about the residuals of the pressure?
some ideas:


Did you try the cellLimited linearUpwindV 1 for div(phi,)?
You can also cellLimit the gradSchemes. Especially for k and omega. If that doesn't help try cellLimited for grad(U) as well...

[calim_cfd]

Originally Posted by olivierG

hello,

Just some hint ...
- Since it's steady state, you may take a look at local time stepping.
- use hex / polyhedre instead of tet mesh

regards,
olivier

as to the elements shapes... yes hex and poly should decrease the mesh size. i ended up with lots of tetra since i was trying out a specific mesher, i could prolly have meshed the same geometry with snappyhexmesh. But since im playing with the issues of large meshes and possible bad ones 2, this mesh is a good example.

and ill try larger time steps. when running steady-state cases i usually forget about this option, but this is a case a can check

thx for tips!

What about the residuals of the pressure?
some ideas:


Did you try the cellLimited linearUpwindV 1 for div(phi,)?
You can also cellLimit the gradSchemes. Especially for k and omega. If that doesn't help try cellLimited for grad(U) as well..

pressure was left apart since i was using 2 correctors..
but here it goes



will do that 2! tyvm!