[jipai]

Hi Foamers,

I'm trying to run an airflow simulation on a theater with OpenFOAM, at a first glance with simpleFoam and then hopefully with buoyantBoussinesqSimpleFoam.

The boundary conditions are as follows :
- Inlet
42 circular inlets : 8,25m/s from the ceiling toward the floor (U fixedValue), p zeroGradient, k fixedValue uniform 0.150, epsilon fixedValue uniform 0.778, nut calculated

- Outlet :
1 rectangular outlet : U zeroGradient, p fixedValue 0, k zeroGradient, epsilon zeroGradient, nut calculated


- Walls :
U noSlip, p zeroGradient, k zeroGradient, epsilon zeroGradient, nut zeroGradient
(I don't care about the flow near the walls, I just wish it doesn't cause divergence in my settings ^^).


I don't succeed in making my solver to converge.

I tried at first to run the simulation in laminar conditions. U solvers doesn't go under 10e-2 and P stays between 0.2 and 0.3. So what could be wrong ?

The resulting airflow isn't that bad. The values are coherent, though a little higher than expected, and the global air circulation is coherent.

Then I tried to turn on turbulence after few iterations. The solver runs for 300 iteration with the sames U and p residuals (10-2 and 0.2-0.3) and then suddenly diverges.


I tried many parameters and also many meshes. I simplified the mesh as much as possible and reduce the cell size to gain precision at the maximum my machine can run.

Here I give my logs :
- checkMesh
- snappyHexMesh
- simpleFoam

--> CheckMesh

Create time

Create polyMesh for time = 1

Time = 1

Mesh stats
points: 13044316
faces: 37910503
internal faces: 37108483
cells: 12438874
faces per cell: 6.031011
boundary patches: 3
point zones: 0
face zones: 0
cell zones: 0

Overall number of cells of each type:
hexahedra: 12298744
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 0
polyhedra: 140130
Breakdown of polyhedra by number of faces:
faces number of cells
6 28002
8 4723
9 92649
10 198
11 102
12 11013
13 110
14 44
15 3207
18 82

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
walls 792580 803925 ok (non-closed singly connected)
inlet 4096 5064 ok (non-closed singly connected)
outlet 5344 5544 ok (non-closed singly connected)

Checking geometry...
Overall domain bounding box (-7.401487e-17 -13.9375 -9.251859e-17) (44.1875 37.5 14.76563)
Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
Mesh has 3 solution (non-empty) directions (1 1 1)
Boundary openness (2.169213e-16 -1.027522e-16 1.313974e-14) OK.
Max cell openness = 3.330669e-16 OK.
Max aspect ratio = 1.00096 OK.
Minimum face area = 0.0002439844. Maximum face area = 0.015625. Face area magnitudes OK.
Min volume = 3.811036e-06. Max volume = 0.001953125. Total volume = 22056.98. Cell volumes OK.
Mesh non-orthogonality Max: 25.24883 average: 2.934891
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 1 OK.
Coupled point location match (average 0) OK.

Mesh OK.

End

--> SnappyHexMesh

Create mesh for time = 0

Read mesh in = 67.8 s

Overall mesh bounding box : (-0.5 -14 -0.5) (45.5 38 15.5)
Relative tolerance : 1e-06
Absolute matching distance : 7.124605e-05

Reading refinement surfaces.
Read refinement surfaces in = 0.02 s

Reading refinement shells.
Read refinement shells in = 0 s

Setting refinement level of surface to be consistent with shells.
Checked shell refinement in = 0 s

Reading features.
Read features in = 0 s


Determining initial surface intersections
-----------------------------------------

Edge intersection testing:
Number of edges : 59039232
Number of edges to retest : 59039232
Number of intersected edges : 457737
Calculated surface intersections in = 77.85 s

Initial mesh : cells:19595264 faces:59039232 points:19849617
Cells per refinement level:
0 19595264

Adding patches for surface regions
----------------------------------

Patch Type Region
----- ---- ------
walls:

1 wall walls

inlet:

2 patch inlet

outlet:

3 patch outlet

Added patches in = 0.73 s

Selecting decompositionMethod none
Layer thickness specified as final layer and expansion ratio.

Refinement phase
----------------

Found point (3.0001 3.0001 1.7777) in cell 2805660 on processor 0

Surface refinement iteration 0
------------------------------

Marked for refinement due to surface intersection : 520 cells.
Marked for refinement due to curvature/regions : 76132 cells.
Determined cells to refine in = 170.83 s
Selected for refinement : 76652 cells (out of 19595264)
Edge intersection testing:
Number of edges : 60808950
Number of edges to retest : 2382322
Number of intersected edges : 706471
Refined mesh in = 54.5 s
After refinement surface refinement iteration 0 : cells:20131828 faces:60808950 points:20554188
Cells per refinement level:
0 19518612
1 613216

Surface refinement iteration 1
------------------------------

Marked for refinement due to surface intersection : 2042 cells.
Marked for refinement due to curvature/regions : 629 cells.
Determined cells to refine in = 2.42 s
Selected for refinement : 3265 cells (out of 20131828)
Edge intersection testing:
Number of edges : 60888069
Number of edges to retest : 131483
Number of intersected edges : 713480
Refined mesh in = 43.5 s
After refinement surface refinement iteration 1 : cells:20154683 faces:60888069 points:20588367
Cells per refinement level:
0 19517369
1 621138
2 16176

/!\ I cut the inbetween iterations

Surface refinement iteration 8
------------------------------

Marked for refinement due to surface intersection : 0 cells.
Marked for refinement due to curvature/regions : 8 cells.
Determined cells to refine in = 2.56 s
Selected for refinement : 8 cells (out of 20186925)
Stopping refining since too few cells selected.


Removing mesh beyond surface intersections
------------------------------------------

Found point (3.0001 3.0001 1.7777) in global region 1 out of 2 regions.
Keeping all cells in region 1 containing point (3.0001 3.0001 1.7777)
Selected for keeping : 12092222 cells.
Edge intersection testing:
Number of edges : 36799461
Number of edges to retest : 686943
Number of intersected edges : 724364

Shell refinement iteration 0
----------------------------

Marked for refinement due to distance to explicit features : 0 cells.
Marked for refinement due to refinement shells : 0 cells.
Determined cells to refine in = 2390.59 s
Selected for internal refinement : 56363 cells (out of 12092222)
Edge intersection testing:
Number of edges : 38070489
Number of edges to retest : 2131171
Number of intersected edges : 776914
Refined mesh in = 30.68 s
After refinement shell refinement iteration 0 : cells:12486763 faces:38070489 points:13105240
Cells per refinement level:
0 11641853
1 760801
2 46709
3 37400

/!\ I cut the inbetween iterations

Shell refinement iteration 99
----------------------------

Marked for refinement due to distance to explicit features : 0 cells.
Marked for refinement due to refinement shells : 0 cells.
Determined cells to refine in = 2.48 s
Selected for internal refinement : 21 cells (out of 13547347)
Edge intersection testing:
Number of edges : 41298225
Number of edges to retest : 1292
Number of intersected edges : 813267
Refined mesh in = 27.97 s
After refinement shell refinement iteration 99 : cells:13547494 faces:41298225 points:14211894
Cells per refinement level:
0 11494674
1 1936296
2 59788
3 56736

Dangling coarse cells refinement iteration 0
--------------------------------------------

Determined cells to refine in = 0.39 s
Selected for refinement : 0 cells (out of 13547494)
Stopping refining since too few cells selected.


Dangling coarse cells refinement iteration 0
--------------------------------------------

Determined cells to refine in = 0.31 s
Selected for refinement : 0 cells (out of 13547494)
Stopping refining since too few cells selected.


Splitting mesh at surface intersections
---------------------------------------

Introducing baffles for 813267 faces that are intersected by the surface.

Edge intersection testing:
Number of edges : 42111490
Number of edges to retest : 5928458
Number of intersected edges : 1609984
Created baffles in = 23.73 s


After introducing baffles : cells:13547494 faces:42111490 points:14211894
Cells per refinement level:
0 11494674
1 1936296
2 59788
3 56736

Introducing baffles to block off problem cells
----------------------------------------------

markFacesOnProblemCells : marked 1074685 additional internal faces to be converted into baffles.
Analyzed problem cells in = 16.46 s


Introducing baffles to delete problem cells.

Edge intersection testing:
Number of edges : 43186175
Number of edges to retest : 3464439
Number of intersected edges : 1610513
Created baffles in = 22.63 s


After introducing baffles : cells:13547494 faces:43186175 points:14211894
Cells per refinement level:
0 11494674
1 1936296
2 59788
3 56736

Remove unreachable sections of mesh
-----------------------------------

Keeping all cells in region 89947 containing point (3.0001 3.0001 1.7777)
Selected for keeping : 12438874 cells.
Edge intersection testing:
Number of edges : 37917743
Number of edges to retest : 0
Number of intersected edges : 802080
Split mesh in = 1188.01 s


After subsetting : cells:12438874 faces:37917743 points:13051401
Cells per refinement level:
0 11140237
1 1217875
2 39658
3 41104

Handling cells with snap problems
---------------------------------

Introducing baffles for 802080 faces that are intersected by the surface.

Edge intersection testing:
Number of edges : 37917743
Number of edges to retest : 2927171
Number of intersected edges : 802080
Created baffles in = 16.07 s


After introducing baffles : cells:12438874 faces:37917743 points:13051401
Cells per refinement level:
0 11140237
1 1217875
2 39658
3 41104

Introducing baffles to block off problem cells
----------------------------------------------

markFacesOnProblemCells : marked 0 additional internal faces to be converted into baffles.
Analyzed problem cells in = 14.35 s


Introducing baffles to delete problem cells.

Edge intersection testing:
Number of edges : 37917743
Number of edges to retest : 0
Number of intersected edges : 802080
Created baffles in = 14.36 s


After introducing baffles : cells:12438874 faces:37917743 points:13051401
Cells per refinement level:
0 11140237
1 1217875
2 39658
3 41104

Remove unreachable sections of mesh
-----------------------------------

Keeping all cells in region 0 containing point (3.0001 3.0001 1.7777)
Selected for keeping : 12438874 cells.
Edge intersection testing:
Number of edges : 37917743
Number of edges to retest : 0
Number of intersected edges : 802080
Split mesh in = 1094.92 s


After subsetting : cells:12438874 faces:37917743 points:13051401
Cells per refinement level:
0 11140237
1 1217875
2 39658
3 41104

Merge free-standing baffles
---------------------------

freeStandingBaffles : detected 0 free-standing baffles out of 0

Detected free-standing baffles : 0
Merged free-standing baffles in = 3.25 s


dupNonManifoldPoints : Found : 1 non-manifold points (out of 13051401)
Edge intersection testing:
Number of edges : 37917743
Number of edges to retest : 0
Number of intersected edges : 802080
Detected unsplittable baffles : 0

Merge refined boundary faces
----------------------------

Merging 6072 sets of faces.

Edge intersection testing:
Number of edges : 37910503
Number of edges to retest : 44164
Number of intersected edges : 794840

Undo iteration 0
----------------
Checking faces in error :
non-orthogonality > 65 degrees : 0
faces with face pyramid volume < 1e-13 : 0
faces with face-decomposition tet quality < 1e-15 : 0
faces with concavity > 80 degrees : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0..1) < 0.02 : 0
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.02 : 0
faces on cells with determinant < 0.001 : 0

Merging all points on surface that
- are used by only two boundary faces and
- make an angle with a cosine of more than 0.7071068.

Removing 6502 straight edge points ...

Edge intersection testing:
Number of edges : 37910503
Number of edges to retest : 47269
Number of intersected edges : 794840

Undo iteration 0
----------------
Checking faces in error :
non-orthogonality > 65 degrees : 0
faces with face pyramid volume < 1e-13 : 0
faces with face-decomposition tet quality < 1e-15 : 0
faces with concavity > 80 degrees : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0..1) < 0.02 : 0
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.02 : 0
faces on cells with determinant < 0.001 : 0

Removing zero-sized patches:
frontAndBack type patch at position 0

Refined mesh : cells:12438874 faces:37910503 points:13044316
Cells per refinement level:
0 11140237
1 1217875
2 39658
3 41104
Writing mesh to time 1
Wrote mesh in = 154.89 s.
Mesh refined in = 8612.52 s.
Checking final mesh ...
Checking faces in error :
non-orthogonality > 65 degrees : 0
faces with face pyramid volume < 1e-13 : 0
faces with face-decomposition tet quality < 1e-15 : 0
faces with concavity > 80 degrees : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0..1) < 0.02 : 0
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.02 : 0
faces on cells with determinant < 0.001 : 0
Finished meshing without any errors
Finished meshing in = 8791.99 s.
End


--> SimpleFOAM

Create time

Create mesh for time = 100


SIMPLE: no convergence criteria found. Calculations will run for 900 steps.

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
No MRF models present

No finite volume options present


Starting time loop

Time = 101

smoothSolver: Solving for Ux, Initial residual = 0.04420976, Final residual = 0.0003398643, No Iterations 9
smoothSolver: Solving for Uy, Initial residual = 0.04553454, Final residual = 0.000331451, No Iterations 9
smoothSolver: Solving for Uz, Initial residual = 0.02992303, Final residual = 0.0002255237, No Iterations 9
GAMG: Solving for p, Initial residual = 0.2121712, Final residual = 0.0001443541, No Iterations 6
GAMG: Solving for p, Initial residual = 0.0007468585, Final residual = 9.9382e-07, No Iterations 13
time step continuity errors : sum local = 1.907021e-07, global = -7.843384e-11, cumulative = -7.843384e-11
ExecutionTime = 33.46 s ClockTime = 54 s

fieldMinMax minMax write:
min(mag(U)) = 0 in cell 2028828 at location (26.39062 23.625 0.109375) on processor 5
max(mag(U)) = 8.286627 in cell 1455994 at location (15.82812 22.73437 14.70312) on processor 4
min(p) = -0.9655955 in cell 2021604 at location (26.32812 23.70312 0.765625) on processor 5
max(p) = 10.91654 in cell 33048 at location (7.0625 26.6875 0.0625) on processor 3

Time = 102

smoothSolver: Solving for Ux, Initial residual = 0.04418991, Final residual = 0.0003376186, No Iterations 9
smoothSolver: Solving for Uy, Initial residual = 0.04544644, Final residual = 0.0003304752, No Iterations 9
smoothSolver: Solving for Uz, Initial residual = 0.02998624, Final residual = 0.0002256606, No Iterations 9
GAMG: Solving for p, Initial residual = 0.2118488, Final residual = 0.0001422935, No Iterations 6
GAMG: Solving for p, Initial residual = 0.0007463951, Final residual = 7.782941e-07, No Iterations 14
time step continuity errors : sum local = 1.49576e-07, global = -5.337561e-11, cumulative = -1.318095e-10
ExecutionTime = 50.01 s ClockTime = 80 s

fieldMinMax minMax write:
min(mag(U)) = 0 in cell 2028828 at location (26.39062 23.625 0.109375) on processor 5
max(mag(U)) = 8.28675 in cell 1455994 at location (15.82812 22.73437 14.70312) on processor 4
min(p) = -0.9651283 in cell 2028845 at location (26.32812 23.70312 0.234375) on processor 5
max(p) = 10.99684 in cell 33048 at location (7.0625 26.6875 0.0625) on processor 3

and so on for 700 iterations (no evolution in the residuals)

[jipai]

I add :
- fvSchemes
- fvSolutions

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 5 |
| \\ / 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,omega) bounded Gauss limitedLinear 1;
div(phi,v2) bounded Gauss limitedLinear 1;
div((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;
}


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

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 5 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
p
{
solver GAMG;
tolerance 1e-06;
relTol 0.001;
smoother GaussSeidel;
minIter 3;
maxIter 100;
}

Phi
{
$p;
}

"(U|k|epsilon|omega|f|v2)"
{
solver smoothSolver;
smoother symGaussSeidel;
tolerance 1e-05;
relTol 0.001;
minIter 3;
maxIter 100;
}
}

potentialFlow
{
nNonOrthogonalCorrectors 10;
}

SIMPLE
{
nNonOrthogonalCorrectors 1;
consistent yes;

residualControl
{
p 1e-5;
U 1e-5;
"(k|epsilon|omega|f|v2)" 1e-5;
}
}

relaxationFactors
{
equations
{
U 0.3; // 0.9 is more stable but 0.95 more convergent
p 0.5;
k 0.7;
epsilon 0.7;
".*" 0.9; // 0.9 is more stable but 0.95 more convergent
}
}


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

[jipai]

Since I'm not used to post on this forum, please ask me if you need some more information about the settings.

Has someone any hints ? It would be great !

[kishpishar]

Your mesh seem to be OK and most of the settings seem to be fine except for the following points:


(1) You ran the solver in laminar flow mode at first - if the flow is turbulent, and in this case very likely it is, you run the risk of getting oscillatory or even diverging solutions.


(2) If you model turbulence using kEpsilon, you'll need to use wall functions on the walls> kqRWallFunction, epsilonWallFunction and nutkWallFunction for k, epsilon and nut fields, respectively.