blockMesh adds wrong defaultfaces
 

I have built a 2D truncated cone with alll faces defined, but after I ran blockMesh it added 6 defaultfaces which cause a high skewness which prevents pimpleFoam to run. The 6 faces seem to be constructed between the front and back planes, which I do not understand why it happened. Are my coordinates not precise enough. The cone has a 54 degree angle at the bottom corners and the different vertices coordinates have many digits. I tried to construct a polyLine at the points in question, but it did not help it either. If I run a 45 degree angled cone I do not have any problem and all coordinate numbers are integers. How can I overcome this problem?

Greetings Klaus and welcome to the forum!

Sorry for the late reply, but only today did I manage to get around to look into your question.

I've taken a somewhat quick look at your "blockMeshDict" and didn't have the time to further diagnose the problem. The best I can do is suggest the following:

• Use the following command:
  Code:

  ---

  paraFoam -block

  ---

  It will help you visually diagnose the "blockMeshDict" you have.
  For more tips on this point of view, have a look at this wiki page: http://openfoamwiki.net/index.php/BlockMesh
• The way you collapsed the edges for the blocks that are "wedges" seems a bit strange to me, when compared to the User Guide: http://www.openfoam.org/docs/user/blockMesh.php:
  
  Quote:

  hex (0 1 2 3 4 5 5 4)

  In comparison, you have this:
  
  Code:

  ---

  hex (12 13 17 17 32 33 37 37)

  ---

  By collapsing the edges too far apart, you might be leading blockMesh into this situation where its not able to properly generate all of the blocks and to merge them.
• You might want to try generating the mesh with only 1 or 2 cells per block, so that it reduces the numerical complexity, at least during a trial-and-error phase.

Best regards,
Bruno


PS: I moved your thread from the technical meshing sub-forum to this "blockMesh" sub-forum, since this is clearly an issue in using blockMesh ;)

blockMesh adds wrong defaultfaces
 

Hi Bruno,

thank you for your review and reply. I had analysed the mesh with paraFoam -block, but I could not really identify solutions to what it showed. Concerning the collapsing, I had just followed the instructions in the user guide for building the blocks which is always in the order of back plane vertices first and then the ones from the front plane. Therefore the resulting block:

hex (12 13 17 17 32 33 37 37).

Your suggestion to manually introduce more blocks at the edges is helpful. I had thought about it too, but did not apply it because of the higher number of vertices and more typing. I was able to have the program find a solution by defining ALL empty faces in the blockMeshDict file and not have blockMesh determine them automatically.

- Klaus