[5tern]

Dear Foamers,

I'm working on an external flow around different shapes. I already tried a sphere, a submarine and various others.
Every time I used snappyHexMesh for meshing and it worked like a charm. Now, I use the same setup like for the sphere and everything else, I only exchanged the .stl-files.

If I run
1) only castellatedMesh: The refinement boxes occur, but no surface refinement. In the log-file I found:

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

Marked for refinement due to surface intersection          : 0 cells.
Determined cells to refine in = 0.02 s
Selected for refinement : 0 cells (out of 7680)
Stopping refining since too few cells selected.

2) castellatedMesh + snap: It snaps perfectly, but again, there's not the specified refinement of the surface.

3) all of it: The layers look awful of course...

I used different .stl's from various meshers, I also checked them with Rhino and Blender and found nothing bad. Also, I loaded the blockMesh and stl at the same time in ParaView and the dimensions and position match.

Currently I am working with version 2.4.0 (it's not possible to upgrade).
Please find my case here: https://www.dropbox.com/s/2p7eukjs69...psoid.zip?dl=0

I would appreciate if somebody could have a look at it and enlighten me :-)
Thank you!

[Antimony]

Hi,

Your blockMesh is too coarse and as a result snappy cannot detect the ellipsoid/determine the cells that have to be refined based on ellipsoid stl.

Double the number of cells in the x & z directions and you will see it working.

Cheers,
Antimony

[5tern]

Thank you very much for your fast reply.
I will give it a try in some minutes.
EDIT: Of course it worked excellently.

So new questions pop up in my mind:

1) I understand that the surface refinement orientates towards the initial blockMesh. Thus, refinement boxes won't help here, correct?

2) Is there an approximation/ a ratio for the relation between the dimensions of the body and cell size of the surrounding mesh? I am just wondering, because the sphere I meshed before had nearly the same dimensions.

Thank you!

[Antimony]

Hi,

You are welcome.

I am no expert at snappyHexMesh, but I will bravely attempt to answer your questions based on my understanding of it.

1. Refinement boxes mainly focus on refining the cells in a volume. Capturing the surface is mainly done (if I am not wrong) in the feature edge refinement and surface refinement.

2. I don't know any such number, but I would guess roughly at least 4 cells in the vicinity of the geometry will help in detecting the geometry.

Cheers,
Antimony

P.S. The go-to-guide for me for snappyHexMesh is this: http://openfoamwiki.net/images/f/f0/...SlidesOFW7.pdf

[5tern]

Thank you! :-)