[anita]

Hi,

I have a 2D case with mesh generation with blockMesh. The solver didn't solve momentum (U) equation. According to this thread http://www.cfd-online.com/OpenFOAM_D...es/1/6884.html
my domain is bent.

I analyzed my mesh and found the problematic block. In this block I use edgeGrading. If I change all ratios to 1 the block is straight. When using combinations of ratios the block gets fatter in the middle.

Parts from blockMeshDict:

convertToMeters 0.001; //mm

vertices
(
//a
(-31.7 9 -0.5) // Vertex a1b = 0
(0.0 9 -0.5) // Vertex a2b = 1
(0.0 15.775 -0.5) // Vertex a3b = 2
(-31.7 15.775 -0.5) // Vertex a4b = 3
(-31.7 9 0.5) // Vertex a1t = 4
(0.0 9 0.5) // Vertex a2t = 5
(0.0 15.775 0.5) // Vertex a3t = 6
(-31.7 15.775 0.5) // Vertex a4t = 7
);

blocks
(

hex (0 1 2 3 4 5 6 7) (50 22 1) edgeGrading (0.25 1 1 0.25 1 4 4 1 1 1 1 1 )//block a
);



CheckMesh: (on z-axis the define points are at
-0.5 mm or 0.5 mm)

Checking geometry...
Domain bounding box: (-0.0317 0.009 -0.000515173) (0 0.015775 0.000515173)
Boundary openness (1.90575e-18 -4.52277e-17 2.57335e-16) OK.
Max cell openness = 2.22755e-16 OK.
Max aspect ratio = 7.16218 OK.
Minumum face area = 4.29135e-08. Maximum face area = 1.16818e-06. Face area magnitudes OK.
Min volume = 4.29163e-11. Max volume = 3.55129e-10. Total volume = 2.17623e-07. Cell volumes OK.
Mesh non-orthogonality Max: 43.2975 average: 31.2745
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 0.418386 OK.
Min/max edge length = 0.000141259 0.00116818 OK.
All angles in faces OK.
Face flatness (1 = flat, 0 = butterfly) : average = 1 min = 1
All face flatness OK.

Mesh OK.

Is this a bug with edgeGrading?

Anita

[hjasak]

Sorry, I don't see the problem: "the block gets fatter in the middle". Can I see this from the picture above?

I originally wrote all this grading stuff, it is used in the pitzDaily simpleFoam tutorial and it works in 2-D without trouble. Can you investigate further?

Hrv

[anita]

Hi Hrv,
you don't see it from the above picture.
I added two pictures looking sideways on the mesh. The z-axis is stretched to see the curved surface better.

You can also see it from the Domain bounding box (-0.0317 0.009 -0.000515173) (0 0.015775 0.000515173) which is larger in z direction as the hex in blockMeshDict.

I also looked in the points file: Only few point at the start and the end of the file have the desired z-position.

Anita

Looking from right side:


Looking from the bottom:

[anita]

Hi,
I looked at the utilitis of OpenFoam and found flattenMesh. This removed the curved surface and now my mesh is real 2D.

Also the solver now solves the U-equation.

By now I can go on with simulating my case, but I still want to now if it was my fault and how I can avoid this problem in future.

Anita

[wolle1982]

Hallo Anita,

I have the same problem that by using the edgeGrading the bounding box gets greater. flattenMesh does NOT remove it, poorly.

And further advice?

[feymark]

Hi,

I can also confirm this behavior for my 3D-cylinder.

/Andreas

[feymark]

For my case the error comes and goes depending on what value I use on the edge.
A value less than 12.5 for instance gives bad behavior and a value greater than 13.2 works well.

Hrv, do you have any clue why this error might occur?

/Andreas

[feymark]

A blockMeshDict like the one below creates this error. The vertices are ordered according to http://www.opencfd.co.uk/openfoam/doc/blockMesh.html .
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 1.5 |
| \ / A nd | Web: http://www.OpenFOAM.org |
| \/ M anipulation | |
/*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 1;
vertices
(
( 0 0 0 ) // vertex number 0
( 1 0 0 ) // vertex number 1
( 1 1 0 ) // vertex number 2
( 0 1 0 ) // vertex number 3
( 0 0 1 ) // vertex number 4
( 1 0 1 ) // vertex number 5
( 1 1 1 ) // vertex number 6
( 0 1 1 ) // vertex number 7
);

blocks
(
hex (0 1 2 3 4 5 6 7) (2 2 2) edgeGrading (4 3 3 4 2 1 1 2 1 1 1 1)
);

edges
(
);

patches
(
);

mergePatchPairs
(
);

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

/Andreas