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-   -   [snappyHexMesh] Geometry disappears when using SnappyHexMesh with multiple blocks (https://www.cfd-online.com/Forums/openfoam-meshing/147920-geometry-disappears-when-using-snappyhexmesh-multiple-blocks.html)

pizzaspinate February 1, 2015 09:03
Geometry disappears when using SnappyHexMesh with multiple blocks
 
2 Attachment(s)
Hey Foamers,

I am facing a problem with my mesh.
I want to simulate a 3d swept wing in a box. The box looks like in the attached picture.
It consists of 3 boxes (upper, middle, lower).
If I run snappyHexMesh I end up with a smaller box outside my stl file (photo also attached).
I don't understand where I went wrong.
Do I have to enter multiple location in mesh points or do I have to merge the patches of my blocks in blockMesh?

Thank you very much in advance for your help!!!!!!!

mturcios777 February 2, 2015 14:31
A few possibilities. If your STL file is not water tight, then you may have issues with the volumes being closed from each other.

Also, when you have the three regions, are you trying to mesh three separate closed domains with snappyHex? If so, you will need to stitch them together afterward. Or, you could use refinement regions to get better resolution on a base mesh without having separate volumes.

pizzaspinate February 3, 2015 08:01
thank you for the reply.

SolidWorks says that there are no open sections so I assume the geometry should be closed.

I try to mesh an aerofoil (it lies in the middle block) and I created the three boxes because I thought it will give me a better mesh ( I wanted to apply a meshing system like you use in ICEM).
The blocks I have created should be already merged together because I created them on shared points. I didnt use merge patches though.

I am generally not sure if multi-blocking is a good strategy to mesh with snappy anyway...

Do you have any recommendations by any chance? Because I am absolutely stuck.

mturcios777 February 3, 2015 12:19
Quote:
Originally Posted by pizzaspinate (Post 530152)
thank you for the reply.

SolidWorks says that there are no open sections so I assume the geometry should be closed.

I try to mesh an aerofoil (it lies in the middle block) and I created the three boxes because I thought it will give me a better mesh ( I wanted to apply a meshing system like you use in ICEM).
The blocks I have created should be already merged together because I created them on shared points. I didnt use merge patches though.

I am generally not sure if multi-blocking is a good strategy to mesh with snappy anyway...

Do you have any recommendations by any chance? Because I am absolutely stuck.
I see. snappyHexMesh uses a different meshing philosphy. If there are boundary patches between the blocks then you will only get the middle section where the aerofoil is (try taking a slice through the middle to confirm this). If what you are after is finer resolution near the aerofoil, then the best method is to use refinementSurfaces and refinementRegions. Look at the snappyHexMesh manual online to find out about how these work:

http://www.openfoam.org/docs/user/snappyHexMesh.php

Good luck!


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