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-   -   High Courant Number @ icoFoam (http://www.cfd-online.com/Forums/openfoam-solving/95674-high-courant-number-icofoam.html)

Artex85 December 28, 2011 12:01

High Courant Number @ icoFoam
 
Dear Foamers!

I designed a raw tetra mesh for a first view over the geometry. I wanted to test the flow with icoFoam. Unfortunately the courant number explodes after a few timesteps. Do you have any ideas how to get this work? Thanks a lot!

checkMesh:
Code:

Exec  : checkMesh
Date  : Dec 29 2011
Time  : 12:51:33
Host  : ubuntu
PID    : 4305
Case  : /home/ubuntu/OpenFOAM/ubuntu-1.5-dev/run/duese_3_tet_icofoam
nProcs : 1

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

Create polyMesh for time = constant

Time = constant

Mesh stats
    points:          17575
    faces:            173802
    internal faces:  159746
    cells:            83387
    boundary patches: 4
    point zones:      0
    face zones:      0
    cell zones:      0

Number of cells of each type:
    hexahedra:    0
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    83387
    polyhedra:    0

Checking topology...
    Boundary definition 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                 
    ColdWall            3374    1772    ok (non-closed singly connected) 
    HotWall            10453    5279    ok (non-closed singly connected) 
    Inlet              93      60      ok (non-closed singly connected) 
    Outlet              136      89      ok (non-closed singly connected) 

Checking geometry...
    This is a 3-D mesh
    Overall domain bounding box (-0.04 -0.0199997 -0.14) (0.02 0.0199993 0)
    Mesh (non-empty) directions (1 1 1)
    Mesh (non-empty, non-wedge) dimensions 3
    Boundary openness (1.76704e-19 2.54345e-19 4.48772e-20) Threshold = 1e-06 OK.
    Max cell openness = 1.54305e-16 OK.
    Max aspect ratio = 12.3272 OK.
    Minumum face area = 1.59421e-07. Maximum face area = 5.57485e-06.  Face area magnitudes OK.
    Min volume = 4.23187e-11. Max volume = 3.34644e-09.  Total volume = 8.00739e-05.  Cell volumes OK.
    Mesh non-orthogonality Max: 58.8765 average: 19.8095 Threshold = 70
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 0.813531 OK.

Mesh OK.

End

fvSolution:
Code:

FoamFile
{
    version    2.0;
    format      ascii;
    class      dictionary;
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p PCG
    {
        preconditioner  DIC;
        tolerance        1e-06;
        relTol          0;
    };

    U PBiCG
    {
        preconditioner  DILU;
        tolerance        1e-05;
        relTol          0;
    };
}

PISO
{
    nCorrectors    2;
    nNonOrthogonalCorrectors 1;
    pRefCell        0;
    pRefValue      0;
}

controlDict:
Code:

FoamFile
{
    version    2.0;
    format      ascii;
    class      dictionary;
    object      controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application icoFoam;

startFrom      startTime;

startTime      0;

stopAt          endTime;

endTime        2;

deltaT          0.02;

writeControl    timeStep;

writeInterval  20;

purgeWrite      0;

writeFormat    ascii;

writePrecision  6;

writeCompression uncompressed;

timeFormat      general;

timePrecision  6;

runTimeModifiable yes;

adjustTimeStep  no;


anon_a December 28, 2011 12:09

What is the value of your Courant number? Have you tried a smaller time step?
You have turned off the adjustable time step by the way, maybe this could help if it was on.
Could you post the log file?

Artex85 December 29, 2011 09:50

Hello anon_a!

Thanks for your quick reply, here is the log file:

Code:

Exec  : icoFoam
Date  : Dec 29 2011
Time  : 13:36:10
Host  : ubuntu
PID    : 5099
Case  : /home/ubuntu/OpenFOAM/ubuntu-1.5-dev/run/duese_3_tet_icofoam
nProcs : 1

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

Create mesh for time = 0

Reading transportProperties

Reading field p

Reading field U

Reading/calculating face flux field phi


Starting time loop

Time = 0.02

Courant Number mean: 0 max: 0 velocity magnitude: 0
PBiCG:  Solving for Ux, Initial residual = 0, Final residual = 0, No Iterations 0
PBiCG:  Solving for Uy, Initial residual = 0, Final residual = 0, No Iterations 0
PBiCG:  Solving for Uz, Initial residual = 1, Final residual = 7.92461e-06, No Iterations 42
PCG:  Solving for p, Initial residual = 1, Final residual = 8.51221e-07, No Iterations 484
PCG:  Solving for p, Initial residual = 0.102054, Final residual = 9.82929e-07, No Iterations 459
time step continuity errors : sum local = 1.31195e-07, global = -3.07613e-10, cumulative = -3.07613e-10
PCG:  Solving for p, Initial residual = 0.054511, Final residual = 8.62196e-07, No Iterations 472
PCG:  Solving for p, Initial residual = 0.466713, Final residual = 8.97311e-07, No Iterations 467
time step continuity errors : sum local = 2.20975e-08, global = 1.92533e-11, cumulative = -2.88359e-10
ExecutionTime = 16.7 s  ClockTime = 17 s

Time = 0.04

Courant Number mean: 0.00506339 max: 3.82497 velocity magnitude: 0.0552267
PBiCG:  Solving for Ux, Initial residual = 0.748645, Final residual = 8.16663e-06, No Iterations 31
PBiCG:  Solving for Uy, Initial residual = 0.771322, Final residual = 9.49122e-06, No Iterations 34
PBiCG:  Solving for Uz, Initial residual = 0.6344, Final residual = 8.92808e-06, No Iterations 39
PCG:  Solving for p, Initial residual = 0.602528, Final residual = 8.92601e-07, No Iterations 488
PCG:  Solving for p, Initial residual = 0.110327, Final residual = 8.24463e-07, No Iterations 459
time step continuity errors : sum local = 5.43346e-07, global = 8.05496e-10, cumulative = 5.17137e-10
PCG:  Solving for p, Initial residual = 0.0449353, Final residual = 8.84106e-07, No Iterations 470
PCG:  Solving for p, Initial residual = 0.461692, Final residual = 8.98988e-07, No Iterations 466
time step continuity errors : sum local = 1.19582e-07, global = -1.29784e-10, cumulative = 3.87353e-10
ExecutionTime = 34.37 s  ClockTime = 34 s

Time = 0.06

Courant Number mean: 0.0263615 max: 13.485 velocity magnitude: 0.19658
PBiCG:  Solving for Ux, Initial residual = 0.764436, Final residual = 9.74761e-06, No Iterations 34
PBiCG:  Solving for Uy, Initial residual = 0.778582, Final residual = 9.481e-06, No Iterations 37
PBiCG:  Solving for Uz, Initial residual = 0.645542, Final residual = 7.43444e-06, No Iterations 40
PCG:  Solving for p, Initial residual = 0.60749, Final residual = 8.64835e-07, No Iterations 488
PCG:  Solving for p, Initial residual = 0.129048, Final residual = 8.77098e-07, No Iterations 457
time step continuity errors : sum local = 3.23187e-06, global = -1.31075e-09, cumulative = -9.234e-10
PCG:  Solving for p, Initial residual = 0.0464013, Final residual = 9.64245e-07, No Iterations 468
PCG:  Solving for p, Initial residual = 0.490751, Final residual = 9.75743e-07, No Iterations 464
time step continuity errors : sum local = 8.02591e-07, global = 2.05433e-09, cumulative = 1.13093e-09
ExecutionTime = 52.24 s  ClockTime = 52 s

Time = 0.08

Courant Number mean: 0.17455 max: 55.7621 velocity magnitude: 0.812884
PBiCG:  Solving for Ux, Initial residual = 0.775338, Final residual = 9.18494e-06, No Iterations 36
PBiCG:  Solving for Uy, Initial residual = 0.780003, Final residual = 8.83473e-06, No Iterations 38
PBiCG:  Solving for Uz, Initial residual = 0.649195, Final residual = 7.62692e-06, No Iterations 40
PCG:  Solving for p, Initial residual = 0.661197, Final residual = 9.82732e-07, No Iterations 479
PCG:  Solving for p, Initial residual = 0.163826, Final residual = 9.35047e-07, No Iterations 442
time step continuity errors : sum local = 2.31072e-05, global = 1.43139e-07, cumulative = 1.4427e-07
PCG:  Solving for p, Initial residual = 0.0544162, Final residual = 9.93518e-07, No Iterations 465
PCG:  Solving for p, Initial residual = 0.535228, Final residual = 9.42873e-07, No Iterations 448
time step continuity errors : sum local = 6.10979e-06, global = -3.08389e-08, cumulative = 1.13431e-07
ExecutionTime = 69.79 s  ClockTime = 70 s

Time = 0.1

Courant Number mean: 1.52184 max: 251.177 velocity magnitude: 3.66159
PBiCG:  Solving for Ux, Initial residual = 0.785002, Final residual = 7.78131e-06, No Iterations 37
PBiCG:  Solving for Uy, Initial residual = 0.775493, Final residual = 7.00292e-06, No Iterations 38
PBiCG:  Solving for Uz, Initial residual = 0.653513, Final residual = 7.65689e-06, No Iterations 39
PCG:  Solving for p, Initial residual = 0.73722, Final residual = 8.38555e-07, No Iterations 487
PCG:  Solving for p, Initial residual = 0.210158, Final residual = 8.81948e-07, No Iterations 458
time step continuity errors : sum local = 0.000179504, global = 6.47978e-09, cumulative = 1.19911e-07
PCG:  Solving for p, Initial residual = 0.0671591, Final residual = 9.26519e-07, No Iterations 469
PCG:  Solving for p, Initial residual = 0.577796, Final residual = 8.43418e-07, No Iterations 464
time step continuity errors : sum local = 5.39014e-05, global = 3.38347e-08, cumulative = 1.53746e-07
ExecutionTime = 88.14 s  ClockTime = 88 s

Time = 0.12

Courant Number mean: 15.771 max: 1213.58 velocity magnitude: 17.2683
PBiCG:  Solving for Ux, Initial residual = 0.791247, Final residual = 4.09263e-06, No Iterations 47
PBiCG:  Solving for Uy, Initial residual = 0.768959, Final residual = 1.95723e-06, No Iterations 53
PBiCG:  Solving for Uz, Initial residual = 0.660241, Final residual = 7.56799e-06, No Iterations 53
PCG:  Solving for p, Initial residual = 0.809628, Final residual = 8.35623e-07, No Iterations 481
PCG:  Solving for p, Initial residual = 0.270383, Final residual = 9.78329e-07, No Iterations 459
time step continuity errors : sum local = 0.00202547, global = 2.30268e-06, cumulative = 2.45642e-06
PCG:  Solving for p, Initial residual = 0.0840898, Final residual = 8.179e-07, No Iterations 468
PCG:  Solving for p, Initial residual = 0.611435, Final residual = 9.48164e-07, No Iterations 464
time step continuity errors : sum local = 0.000754444, global = -2.30185e-07, cumulative = 2.22624e-06
ExecutionTime = 107.21 s  ClockTime = 107 s

Time = 0.14

Courant Number mean: 203.818 max: 6315.59 velocity magnitude: 144.106
PBiCG:  Solving for Ux, Initial residual = 0.799529, Final residual = 7.23114e-06, No Iterations 118
PBiCG:  Solving for Uy, Initial residual = 0.768657, Final residual = 8.52382e-06, No Iterations 119
PBiCG:  Solving for Uz, Initial residual = 0.67574, Final residual = 6.44984e-06, No Iterations 123
PCG:  Solving for p, Initial residual = 0.644255, Final residual = 9.53304e-07, No Iterations 501
PCG:  Solving for p, Initial residual = 0.124882, Final residual = 8.26806e-07, No Iterations 468
time step continuity errors : sum local = 0.0255069, global = -5.32141e-06, cumulative = -3.09518e-06
PCG:  Solving for p, Initial residual = 0.0625569, Final residual = 9.64602e-07, No Iterations 485
PCG:  Solving for p, Initial residual = 0.476678, Final residual = 9.36606e-07, No Iterations 483
time step continuity errors : sum local = 0.00664253, global = -2.03334e-05, cumulative = -2.34285e-05
ExecutionTime = 134.23 s  ClockTime = 134 s

Time = 0.16

Courant Number mean: 1224.81 max: 5.8799e+06 velocity magnitude: 95137.2
PBiCG:  Solving for Ux, Initial residual = 0.995393, Final residual = 0.0200732, No Iterations 1000
PBiCG:  Solving for Uy, Initial residual = 0.991433, Final residual = 0.307995, No Iterations 1000
PBiCG:  Solving for Uz, Initial residual = 0.985122, Final residual = 0.0269352, No Iterations 1000
PCG:  Solving for p, Initial residual = 0.929687, Final residual = 11.7345, No Iterations 1000
PCG:  Solving for p, Initial residual = 0.794915, Final residual = 2.26295, No Iterations 1000
time step continuity errors : sum local = 3.50337e+06, global = 10532.6, cumulative = 10532.6
PCG:  Solving for p, Initial residual = 0.969994, Final residual = 1.9792, No Iterations 1000
PCG:  Solving for p, Initial residual = 0.680809, Final residual = 4.05222, No Iterations 1000
time step continuity errors : sum local = 1.599e+09, global = 1.22747e+07, cumulative = 1.22852e+07
ExecutionTime = 238.53 s  ClockTime = 239 s

Time = 0.18

Courant Number mean: 9.19732e+08 max: 1.85522e+12 velocity magnitude: 7.06915e+10
PBiCG:  Solving for Ux, Initial residual = 0.999745, Final residual = 9.62717, No Iterations 1000
PBiCG:  Solving for Uy, Initial residual = 0.999748, Final residual = 10.851, No Iterations 1000
PBiCG:  Solving for Uz, Initial residual = 0.999861, Final residual = 2.88039, No Iterations 1000
PCG:  Solving for p, Initial residual = 1, Final residual = 196.18, No Iterations 1000
PCG:  Solving for p, Initial residual = 0.843622, Final residual = 5.02074, No Iterations 1000
time step continuity errors : sum local = 2.12167e+18, global = 4.6608e+09, cumulative = 4.67308e+09
PCG:  Solving for p, Initial residual = 0.922669, Final residual = 2.7607, No Iterations 1000
PCG:  Solving for p, Initial residual = 0.873783, Final residual = 3.07253, No Iterations 1000
time step continuity errors : sum local = 3.67336e+20, global = 4.99835e+15, cumulative = 4.99835e+15
ExecutionTime = 341.26 s  ClockTime = 341 s

Time = 0.2

Courant Number mean: 2.28604e+20 max: 8.40228e+23 velocity magnitude: 3.89946e+22
PBiCG:  Solving for Ux, Initial residual = 0.999885, Final residual = 6.49499, No Iterations 1000
PBiCG:  Solving for Uy, Initial residual = 0.999815, Final residual = 3.9282, No Iterations 1000
PBiCG:  Solving for Uz, Initial residual = 0.999772, Final residual = 2.70425, No Iterations 1000
PCG:  Solving for p, Initial residual = 1, Final residual = 57.7895, No Iterations 1000
PCG:  Solving for p, Initial residual = 0.771788, Final residual = 124.919, No Iterations 1000
time step continuity errors : sum local = 4.00756e+33, global = 5.1915e+25, cumulative = 5.1915e+25
PCG:  Solving for p, Initial residual = 0.923169, Final residual = 4.28131, No Iterations 1000
PCG:  Solving for p, Initial residual = 0.74075, Final residual = 392.082, No Iterations 1000
time step continuity errors : sum local = 1.39632e+38, global = -1.04069e+30, cumulative = -1.04064e+30
ExecutionTime = 446.61 s  ClockTime = 447 s

Time = 0.22

Courant Number mean: 6.86548e+37 max: 1.692e+42 velocity magnitude: 6.1894e+40
PBiCG:  Solving for Ux, Initial residual = 0.999959, Final residual = 2.91466, No Iterations 1000
PBiCG:  Solving for Uy, Initial residual = 0.999976, Final residual = 0.549805, No Iterations 1000
PBiCG:  Solving for Uz, Initial residual = 0.99999, Final residual = 0.420483, No Iterations 1000
PCG:  Solving for p, Initial residual = 1, Final residual = 248.252, No Iterations 1000
PCG:  Solving for p, Initial residual = 0.0273632, Final residual = 0.0501284, No Iterations 1000
time step continuity errors : sum local = 1.22223e+60, global = 1.90958e+44, cumulative = 1.90958e+44
PCG:  Solving for p, Initial residual = 0.132324, Final residual = 1.12506, No Iterations 1000
PCG:  Solving for p, Initial residual = 0.0522075, Final residual = 0.24675, No Iterations 1000
time step continuity errors : sum local = 1.9022e+63, global = -1.83909e+50, cumulative = -1.83909e+50
ExecutionTime = 551.96 s  ClockTime = 552 s

Time = 0.24

Courant Number mean: 1.41686e+63 max: 2.14683e+67 velocity magnitude: 7.26454e+65
PBiCG:  Solving for Ux, Initial residual = 0.999941, Final residual = 5.11203, No Iterations 1000
PBiCG:  Solving for Uy, Initial residual = 0.99994, Final residual = 0.204469, No Iterations 1000
PBiCG:  Solving for Uz, Initial residual = 0.999928, Final residual = 1.03388, No Iterations 1000
PCG:  Solving for p, Initial residual = 1, Final residual = 3.266, No Iterations 1000
PCG:  Solving for p, Initial residual = 1.9343e-11, Final residual = 1.9343e-11, No Iterations 0
time step continuity errors : sum local = 1.47482e+88, global = -3.62724e+71, cumulative = -3.62724e+71
PCG:  Solving for p, Initial residual = 3.87133e-11, Final residual = 3.87133e-11, No Iterations 0
PCG:  Solving for p, Initial residual = 3.87133e-11, Final residual = 3.87133e-11, No Iterations 0
time step continuity errors : sum local = 2.95171e+88, global = -2.1468e+72, cumulative = -2.50952e+72
ExecutionTime = 633.62 s  ClockTime = 634 s

Time = 0.26

Courant Number mean: 8.67119e+87 max: 2.38864e+92 velocity magnitude: 8.00775e+90
PBiCG:  Solving for Ux, Initial residual = 0.999973, Final residual = 0.645976, No Iterations 1000
PBiCG:  Solving for Uy, Initial residual = 0.99999, Final residual = 0.272165, No Iterations 1000
PBiCG:  Solving for Uz, Initial residual = 0.999979, Final residual = 0.313018, No Iterations 1000
PCG:  Solving for p, Initial residual = 1, Final residual = 11.673, No Iterations 1000
PCG:  Solving for p, Initial residual = 2.40327e-11, Final residual = 2.40327e-11, No Iterations 0
time step continuity errors : sum local = 1.46936e+101, global = 1.28168e+98, cumulative = 1.28168e+98
PCG:  Solving for p, Initial residual = 7.36934e-11, Final residual = 7.36934e-11, No Iterations 0
PCG:  Solving for p, Initial residual = 7.36934e-11, Final residual = 7.36934e-11, No Iterations 0
time step continuity errors : sum local = 4.5056e+101, global = 1.7056e+98, cumulative = 2.98729e+98
ExecutionTime = 718.06 s  ClockTime = 718 s

Time = 0.28

Courant Number mean: 1.45564e+101 max: 9.1374e+104 velocity magnitude: 3.16353e+103
Floating point exception (core dumped)

cheers

Tarak December 29, 2011 20:57

Hii,

Please check the quality of your mesh using the checkMesh utility, and judge whether the relevant parameters (e.g aspect ratio) look good or not.

Thanks,
Tarak

vinz December 30, 2011 04:35

you can also run your computation by specifying a maximum courant number of 1 or 2, instead of specifying the time step.

This way, the time step will be adapted directly to avoid courant number being higher than the value you specify. At least, as long as possible.

Tarak December 30, 2011 04:37

You can also try the following link. It shows how to use an adjustable time step depending on the Courant No.
http://www.idurun.com/?p=371

Artex85 December 30, 2011 04:59

Dear Foamers!

After the problems with the tet mesh, i designed a simple pipe with hexas to check the openfoam mesh files which are created out of pointwise. checkMesh is just Fine, courent number with icoFoam is ... yea going up. If i change the ncorrectors to zero the courant number is stable.
I tried to modify the icoFoam solver to be adjustable for the timesteps, dont get it worked.

anon_a January 3, 2012 04:26

Could you check your link? I don't have access to the file

hossein4433 January 3, 2012 04:36

Hi
i write a loop in my UDF by C_FACE_loop. its worked in 3D but in 2D in fluent show this error "non-integer subscript expression: unsigned char"
whats that mean?
please help me to solve this
thanks

Artex85 January 3, 2012 09:06

Done
 
Dear Foamers!

The hex pipe is working, problem was the small cell size in combination with a too large timestep.

The tet pipe is still pending, I think there is a problem with the mesh.

The helix is done.

All downloadable here -->

Pipe meshes with pointwise
Working hex pipe
Crashing tet pipe
helix mesh with pointwise


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