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Brunno March 2, 2010 14:30

snappyHM - Boundary layer issue
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I am working on a test case of a swirl atomizer for propulsion applications. Despite those well-known edge problems, snappyHM works fine for the most part. So far, I can't figure out how to make the boundary layer "grow" on the entire cylindrical patch and minuscule tangential channel walls (see attached figure and addLayers settings). It seems that BL attaches only when the mesh is coarse. Does anyone have a clue ?
Any help is greatly appreciated.

bjr March 2, 2010 16:05

I'm working on similar issues, but am a little behind you. I will be investigating some of your layer control settings on my cylinder case asap.

bjr March 2, 2010 16:05

Did you ever get boundary layer resolution and viscous drag results you liked?

Brunno March 2, 2010 16:29

snappyHM - Boundary layer issue
Hello ben,

Thank you for the response.
Boundary layer resolution was acceptable on previous test cases. I am currently running the inviscid, single-phase flow case, so I don't have any viscous results at hand.

bjr March 2, 2010 16:41

Is there any chance you could provide any said test cases? I'm really looking to put together a case that starts from just an stl file, a blockMeshDict, and a snappyHexMeshDict that potentially yield good drag results. I think this would be a highly valuable starting point for many out there without access to commercial gridding tools to start learning quickly.

I have a location that large files can be publicly uploaded and downloaded from if needed.

I totally understand if you don't have the chance/time though... days are short.

Many thanks,
Ben Racine

bjr March 2, 2010 19:42

Brunno kindly supplied me with this orifice case...

Mo-ITB May 4, 2010 05:43

sorry, i did a mistake in paraview, the mesh was even worse in 1.6.x

linnemann May 6, 2010 03:45


What is the maximum cell limit in the snappy dict?

I had similar problems once and upping the local and global cell limit made it possible to get the desired mesh.

The entries are there to prevent an explosion in cell count.

openfoam_user July 22, 2010 06:03

Hi Bruno,

did you solve you problem ? How ?

I have encountered the same problem and don't know what to do until now ?

I get layers only where there is more refinement !



Brunno July 22, 2010 06:29

snappyHM - Boundary layer issue
Hello Stephane,

Yes, I did solve the problem - not exactly through snappyHexMesh, but using a combination of adaptive mesh (see the dictionaries cellSetDict and refineMeshDict) based on the gradient of velocity (magU) and snappyHM. The results are not always acceptable - it's usually a trial-and-error process, but it worked for me.

Good luck !

openfoam_user July 22, 2010 06:36

Hi Brunno,

thanks for your advice.

I think that the problem for me is a little bit different. I would like to add several layers around my body in order to obtain Y+ near 1, if possible.


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