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-   -   [blockMesh] Courant in axisymmetric simulations (https://www.cfd-online.com/Forums/openfoam-meshing/213200-courant-axisymmetric-simulations.html)

 arsimons December 18, 2018 09:49

Courant in axisymmetric simulations

Hi foamers

I am currently trying to simulate an axis-symmetrical set-up using wedge. Because of the wedge-like shape, some cells become very small. I tried to solve this using the simpleGrading which makes the cells near the axis longer (in r-direction) than the cells further away from the axis. However, I still get very long calculation times.

Is there any other method which I can apply to reduce the calculation time?

I am using a wedge of 1°, so the cells are also very thin. I could increase this to 5 degrees, but I am not sure whether:
- the calculation time will decrease significantly?
- this has any influence on the accuracy of the simulation?

Best regards
Arne

 yambanshee March 6, 2019 02:44

Is your mesh 2d, or 3d? What does meshCheck say?

 arsimons March 6, 2019 03:26

Hi yambanshee

My mesh is 2D, which I thought was obligated when using the wedge-boundary conditions?

I did not try checkMesh yet, my mesh works since the calculations run, they just run very slowly because of the Courant Number in the cells at the axis.
I will try checkMesh immediatly and I will let you know the results.

Best regards
Arne

__________________________________________________ __________________________________________________ ________________________________

EDIT: I just tried checkMesh and he results are below. This mesh was made with blockMesh and had a simpleGrading of (1 1 1).

/*---------------------------------------------------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1806 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
Build : v1806
Arch : "LSB;label=32;scalar=64"
Exec : checkMesh
Date : Mar 06 2019
Time : 09:26:36
Host : "ea10c417"
PID : 672
I/O : uncollated
Case : /mnt/c/Users/arsimons/Documents/OpenFOAM_local/simulaties/AA_Geometry/Wedge
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: 20301
internal points: 0
faces: 40050
internal faces: 19750
cells: 10000
faces per cell: 5.98
boundary patches: 6
point zones: 0
face zones: 0
cell zones: 0

Overall number of cells of each type:
hexahedra: 9800
prisms: 200
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 0
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
axis 0 0 ok (empty)
rightWall 200 402 ok (non-closed singly connected)
lowerWall 50 101 ok (non-closed singly connected)
atmosphere 50 101 ok (non-closed singly connected)
back 10000 10251 ok (non-closed singly connected)
front 10000 10251 ok (non-closed singly connected)

Checking faceZone topology for multiply connected surfaces...
No faceZones found.

No cellZones found.

Checking geometry...
Overall domain bounding box (0 0 -0.0174) (0.05 0.2 0.0174)
Mesh has 2 geometric (non-empty/wedge) directions (1 1 0)
Mesh has 3 solution (non-empty) directions (1 1 1)
Wedge back with angle 19.1879 degrees
Wedge front with angle 19.1879 degrees
All edges aligned with or perpendicular to non-empty directions.
Boundary openness (7.25056e-14 -3.85576e-18 1.36653e-17) OK.
Max cell openness = 2.21273e-16 OK.
Max aspect ratio = 2 OK.
Minimum face area = 3.48e-07. Maximum face area = 3.48e-05. Face area magnitudes OK.
Min volume = 3.48e-10. Max volume = 3.4452e-08. Total volume = 0.000174. Cell volumes OK.
Mesh non-orthogonality Max: 0 average: 0
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 0.869726 OK.
Coupled point location match (average 0) OK.

Mesh OK.

End

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