Snappy: cell normal orientation on open surface
 

Hello everybody,

When i use snappyHexMesh on a surface which isn't a closed one I have a problem with cell normals orientation: it isn't uniform on the surface (kind of random between 1 or -1). Normals are well oriented on my .stl file.

Do you know a way to harmonize cell normals orientation after meshing ?

Or maybe SnappyHexMesh isn't confortable with open surface?

Hi Nolwenn,
I have the same problem, I'd like to have uniform cellNormal in some faceZones inside my volume.
I tried renumberMesh but without complete success.
Did you found a solution for your problem?

Andrea

Hello Andrea,

No, for the moment I didn't make any progress with this.
Can you tell me if you find something interesting ?

Cheers

Nolwenn

You can see my problem in attached picture,
I'd like to calculate the mass flow rater throgh a faceZone.
The problem is the cellNormal in Z direction are random! (In my starting .stl the normals are uniform).
So if I calculate the mass flow rate with OF function sum(phi) I got error.
I'm thinking to calculate it like sum(phi*sign(normal)).
Do you know if the normal is exportable like a field? I can see it in paraview but I don't see anything in my time or constant directory (I think paraview elaborate it depending on nodes numbering)

Andrea

Hi,
I have the same problem. Did you ever find out how to reset the surface normals?
Regards
Stefanie

Hi,
Nothing new ... I extract the values from neighbours cells during post processing.

Nolwenn

Also, I have same problem.

So, Does anyone know how to use surfaceOrient utility?

I solved this problem from surfaceOrient utility
surfaceOrient <surfaceFile> <visiblePoint> <output surface file>

I solved this problem from surfaceOrient utility

Hello,

Could you please help, what is the meaning of <visiblePoint> in your post, I am really finding it hard to use this utility. Any comment/suggestion would be a great help, thanks in advance.

Hi,


Does the documentation helps?
https://www.openfoam.com/documentati...aceOrient.html


Cheers,
Yann

Thanks Yann for your help, but could not figure out the , what is this referring to ? Could you please explain what that is, any further comment will help me a lot, thanks in advance.

Hi,

It's just a point outside of your geometry, used by the utility do define what is "outside" the geometry and orient the normals accordingly.

So pretty much any coordinate not located inside your geometry will do. (You can set a point very far and that's it).

Of course surfaceOrient will not work if your surface is not closed.

Cheers,
Yann

Thanks a lot Yann for your help, so this point should be outside the "bounding box" or "geometry" without considering any orientation etc ? Sorry for the multiple posts and for being so naive. Thank you very much for your help.

It should be anywhere outside the volume of your surface file. It's just a point coordinates so there is not any notion of orientation.

Once you give this point, surfaceOrient knows which side of the surface is "outside" and which is "inside" and it will set the face normals accordingly.

Cheers,
Yann

Thanks a lot Yann, using your help and guidance I am able to use this utility and achieved the desired goal of proper orientation.