CFD Online Discussion Forums - [snappyHexMesh] Controlling y+ values with snappyHexMesh?

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- - [snappyHexMesh] Controlling y+ values with snappyHexMesh? (https://www.cfd-online.com/Forums/openfoam-meshing/85322-controlling-y-values-snappyhexmesh.html)

I see in the roadmap of cfMesh is to add anisotropic refinement so hopefully not long!!

I think for now I will try using the potentialfreesurfacefoam solver and calculate viscous drag by hand. Think this method should be sufficient for comparative studies.

Its surprising that the OpenCFD guys doing openFoam have not improved the snappyHexMesh reliability? Especially considering they make their money by customers paying for specific developments, I wonder why someone has not paid for this improvement to snappy? Perhaps they know it is fundamentally flawed and that is why they have begun developing foamyQuadMesh?

Dear Eric, James,

Eric, thank you for your kind word regarding cfMesh.
James, I am aware that anisotropic refinement is important for marine applications. Hence, we have already done work in that respect, and we plan to release it with the next release of cfMesh.

Regards,

Franjo

any rough ETA on when the next release will be??

Dear James, our next release is scheduled for the 2nd half of April, we'll announce it on the forum as well.

deal seaspray.
I like your Bash scripts. But it says 'Insufficient permissions'. I don't konw much about ubuntu. could you give me some ideas?
thanks.

It sounds like you are trying to write to a location where permissions don't allow you to do so, or execute a script that is lacking the executable attribute. Try chmod +x filename on the script to make it executable maybe.

Quote:

Originally Posted by seaspray (Post 491628)

Robo,

I have never run into this error so far within this context. Is it a result of refining to an extremely thin inner layer (it almost sounds like it), i.e. near the end of the process, or does it happen at the start?

Because I have split my SHM process into a snap and then layer grow phase, when I set up a new environment (new background mesh, different size geometry) I visually inspect the snapped mesh and the grown layer before refining.
Once this has been done, I can normally substitute geometries without looking at the mesh, but keep in mind that I always mesh the "same kind of stuff" more or less. If I suddenly introduced something much more exotic and complicated, it might not go that well without at least reviewing the parameters for SHM.

I do however remember refineWallLayer failing - possibly with this error - when I tried refining meshes that had not been intended for that, i.e. bad multi-layer meshes from SHM, meshes that weren't wall parallel etc.

I would suggest going back and checking the previous stages and then also making sure you are not trying to refine down to incredibly thin layers, which happens very quickly with geometric progressions.
If you look above, in Pete's Python script, he coded 18 layers with a growth ratio of 1.25: that is a ratio of 55 between the thickest and thinnest layer... this could be a tough test.

I try to work out roughly what y+ = 1 should look like in the regions of interest and I try to approach this value with the refinement and no more. The thickness of my original SHM-grown layer is calculated to more or less contain the entire boundary layer (99% freestream velocity) where I want it solved rather than bridged by wall functions. At the moment I am using 8-9 mesh layers with a growth ratio of 1.25 to resolve the boundary layer and it seems to be behaving for the size of problems I am dealing with, but it may not be the final word.

I am trying your script on a quadcopter. The layer addition doesn't seems to work well using SHM.

I have placed the script file under home/openFOAM/bin. So, I should try to add a single layer before executing your script right?

Ashish,

From memory, my script refined an existing single wall layer, so it needed to be created first by SHM. However, one key issue with the approach was that the OpenFOAM wall layer refinement utility didn't check/correct the mesh for quality. If you get a bad mesh, the solver crashes.

Use cfMesh instead.

Best regards,

Eric