[Harak]

Hey,

I want to create a quadrisected cylinder with blockMesh, like this:


What I've done so far is that I created a block with fewer than 8 vortices:



My question is, based on what do I have to define the 3 values in arc in the brackets, for example, arc 3 6 (? ? ?).

Thanks!

This is my blockMeshDict:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | foam-extend: Open Source CFD                    |
|  \\    /   O peration     | Version:     3.1                                |
|   \\  /    A nd           | Web:         http://www.extend-project.de       |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 1;

vertices
(
    (0 0 0)
    (1 0 0)
    (0 1 0)
    (1 1 0)
    (0 0 1)
    (1 0 1)
    (0 1 1)
    (1 1 1)
);

blocks
(
    hex (1 1 3 3 4 5 7 6) (10 10 10) simpleGrading (1 1 1)
);

edges
(
    //arc 3 6 (? ? ?)
    //arc 1 4 (? ? ?)

);

patches
(
    empty frontAndBackPlanes
    (
        (1 3 3 1)
    )
);

mergePatchPairs
(
);

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

[alexB]

Hi Harak,

first off all, does your blockmeshdict run well?
As written in the UserGuide ( http://cfd.direct/openfoam/user-guide/blockMesh/ ) you shouldn't let collapse thethe first defined vertices of your block, because they also define your coordinate system. Perhaps that never will be a problem while running your case.

Now to your posted problem.
For simple geometries as yours I would propose to just use a calculator to determine the interpolation point.
You want to describe an arc in the x-z-plane.
Many arcs are possible to connect Point 3 and 6.
With the interpolation point you chose one specific arc.
With an interpolation point in the x-z-plane that also contain 3 and 6 you choose an arc in this plane.
To make it short:
take ( sin(45) 1 cos(45) )

regards
Alex

[Harak]

Originally Posted by alexB

Hi Harak,

first off all, does your blockmeshdict run well?
As written in the UserGuide ( http://cfd.direct/openfoam/user-guide/blockMesh/ ) you shouldn't let collapse thethe first defined vertices of your block, because they also define your coordinate system. Perhaps that never will be a problem while running your case.

Now to your posted problem.
For simple geometries as yours I would propose to just use a calculator to determine the interpolation point.
You want to describe an arc in the x-z-plane.
Many arcs are possible to connect Point 3 and 6.
With the interpolation point you chose one specific arc.
With an interpolation point in the x-z-plane that also contain 3 and 6 you choose an arc in this plane.
To make it short:
take ( sin(45) 1 cos(45) )

regards
Alex

Hi Alex,

thanks for your reply!

Yes, my blockMeshDict is working well without any errors.
I tried

arc 3 6 (0.70710678 1 0.70710678)
arc 1 4 (0.70710678 1 0.70710678)

but unfortunately it seems that nothing happened.

Can you please explain what the rule of defining these three values is?
I've already read through this thread (http://www.cfd-online.com/Forums/ope...blockmesh.html) but didn't get it neither.

I appreciate your help!

[amod_kumar]

Hi,

I corrected
arc 3 6 (0.70710678 1 0.70710678)
arc 1 4 (0.70710678 1 0.70710678)

to
arc 3 6 (0.70710678 1 0.70710678)
arc 1 4 (0.70710678 0 0.70710678) //vertices 1 & 4 are at y=0

It created arc and generated the mesh but highly skewed. You may like to review the co-ordinates to define the arc. The mesh is attached.

Regards,

[Harak]

Originally Posted by Harak

Hi Alex,

thanks for your reply!

Yes, my blockMeshDict is working well without any errors.
I tried

arc 3 6 (0.70710678 1 0.70710678)
arc 1 4 (0.70710678 1 0.70710678)

but unfortunately it seems that nothing happened.

Can you please explain what the rule of defining these three values is?
I've already read through this thread (http://www.cfd-online.com/Forums/ope...blockmesh.html) but didn't get it neither.

I appreciate your help!

Nevermind, just solved the problem.
The reason it didn't work was because of what you said here:

you shouldn't let collapse thethe first defined vertices of your block, because they also define your coordinate system

My origin was my 0-vertice, so I just changed the numbering so that my first defined vertice does not collapse anymore!

Thank you sooo much!

[alexB]

You are welcome Harak,

the rule behind the definition of an arc is simple.
The three values are the x,y and z coordinates of one additional point on the arc.

Because an arc is defined completely by three different points on this arc.
Just imagine two arbitrary points in 3-dimensional space.
If its clear that the connecting line is an arc, every additional point defines another arc.

@amod:
I suggest you just helped Harak and are not hung at the same point.

regards
Alex

[amod_kumar]

Hello,
Out of curiosity, I tried
hex (0 4 1 1 2 6 3 3) (10 10 10) simpleGrading (1 1 1)

It generated the correct geometry and mesh. Though I would recommend to use Y-block and further divide the sector into 3 sub-sector as shown below. I will not only eliminate the need of collapsed blocks but a high-quality mesh can also be generated with ease.

Regards,
Amod

[Harak]

Originally Posted by amod_kumar

Hello,
Out of curiosity, I tried
hex (0 4 1 1 2 6 3 3) (10 10 10) simpleGrading (1 1 1)

It generated the correct geometry and mesh. Though I would recommend to use Y-block and further divide the sector into 3 sub-sector as shown below. I will not only eliminate the need of collapsed blocks but a high-quality mesh can also be generated with ease.

Regards,
Amod

Your idea sounds pretty smart, though my configuration fits my case well enough

[dinesh1700]

i am facing problem in defining arc in wedge type of problem. without the arc option the mesh is running fine but as i include an arc mesh problem arises
blockmeshdict file is as follows:

Capture.JPG

[amod_kumar]

Hello Dinesh,
Can you attached your blockMeshDict as txt file?

[dinesh1700]

sir the blockMesh file is attached i am struggling with this from last 2 weeks still not able to find the error in arc syntax.

thanks

[amod_kumar]

Hello Dinesh,
I do not think there is any issue with the arc. The wedge is such a small angle 1.5 [deg] that is looks a straight line. If you zoom very closely in ParaView, the arc is visible. Try changing

hex ( 0 1 5 4 0 1 2 3) (400 50 2) SimpleGrading (1 0.2 1)

to

hex ( 0 1 5 4 0 1 2 3) (400 50 8) SimpleGrading (1 0.2 1)

and then check.

I also realized that the blockMesh does not work if wedge angle is > 15 [deg].

Regards,
Amod

[dinesh1700]

the problem i am solving is laminar flow in a pipe , but i am getting same velocity profile everywhere. i am attaching other files.