How do you handle multiple blocks?

murrdpirate · May 19, 2011, 21:32

I'm trying to create a room with an inlet (i.e. diffuser) and outlet, so I broke the room up into 7 blocks as you can see in this image: http://imgur.com/JzgmP

I believe I successfully made patches on all the boundaries, but my problem appears to be that the block faces in the interior are not being treated correctly. I thought I could just leave them as empty, but apparently you can only do that with 2D meshes. Any help would be greatly appreciated.

Bernhard · May 20, 2011, 01:46

There are no true 2D meshes in OpenFOAM. Do the grids match on the opposite sides of a internal edge?

murrdpirate · May 20, 2011, 02:03

Right, if I recall from the user's guide, a 2D problem is basically faked by assigning "empty" patches to the block faces in the third dimension. I thought that I could apply this to my interior faces, but I get an error saying I can't because my geometry is 3 dimensional.

I'm not sure what you mean in your second question. I'm able to run blockMesh at least, but I can run the solution. Not sure if that answers your question.

Maybe I'm going about this the wrong way? I just want a box with a small inlet and outlet. I tried doing that with one big block and multiple patches, but that didn't seem to work either.

Thanks for the response.

Bernhard · May 20, 2011, 02:15

You cannot use empty patch in three dimensions. Because a 2D mesh is treated as a 3D mesh with only one cell in the third direction, that why you take these patches to be empty, because there is nothing to calculate.

You don't have to name the internal faces. All interior faces that you do not name in a patch, are automatically treated as a internal face. All boundary faces get collected in the patch defaultWalls or something. In blockMesh you can leave the patches subdictionary empty, and then check your mesh. If everything is OK, you can continue naming the boundary faces as wall or patch, but not as empty!

murrdpirate · May 20, 2011, 09:56

I could have sworn that's what I did in my first attempt, and that it kept automatically placing the unpatched block faces into default, empty patches. But I must have been doing something else wrong, because what you say definitely makes sense.

I'm at work at the moment, but I'll give it another shot asap. Thank you very much for your help!

murrdpirate · May 20, 2011, 14:25

Your first instinct was correct; the meshes were not matching on both sides of all the interior faces. I finally seem to have it working now.

I think that because the meshes didn't match, the program was trying to get me to apply some boundary conditions to them. Or maybe not...I'm really not sure. Either way, thanks again for the help. This is my first non-tutorial case and I felt like I was on my last leg.

May 19, 2011, 21:32	How do you handle multiple blocks?	#1
murrdpirate Member Kevin Join Date: May 2011 Posts: 33 Rep Power: 14	I'm trying to create a room with an inlet (i.e. diffuser) and outlet, so I broke the room up into 7 blocks as you can see in this image: http://imgur.com/JzgmP I believe I successfully made patches on all the boundaries, but my problem appears to be that the block faces in the interior are not being treated correctly. I thought I could just leave them as empty, but apparently you can only do that with 2D meshes. Any help would be greatly appreciated.

May 20, 2011, 01:46		#2
Bernhard Senior Member Bernhard Join Date: Sep 2009 Location: Delft Posts: 790 Rep Power: 21	There are no true 2D meshes in OpenFOAM. Do the grids match on the opposite sides of a internal edge? murrdpirate likes this. Last edited by Bernhard; May 20, 2011 at 02:10.

May 20, 2011, 02:15		#4
Bernhard Senior Member Bernhard Join Date: Sep 2009 Location: Delft Posts: 790 Rep Power: 21	You cannot use empty patch in three dimensions. Because a 2D mesh is treated as a 3D mesh with only one cell in the third direction, that why you take these patches to be empty, because there is nothing to calculate. You don't have to name the internal faces. All interior faces that you do not name in a patch, are automatically treated as a internal face. All boundary faces get collected in the patch defaultWalls or something. In blockMesh you can leave the patches subdictionary empty, and then check your mesh. If everything is OK, you can continue naming the boundary faces as wall or patch, but not as empty! murrdpirate likes this.

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May 20, 2011, 02:03		#3
murrdpirate Member Kevin Join Date: May 2011 Posts: 33 Rep Power: 14	Right, if I recall from the user's guide, a 2D problem is basically faked by assigning "empty" patches to the block faces in the third dimension. I thought that I could apply this to my interior faces, but I get an error saying I can't because my geometry is 3 dimensional. I'm not sure what you mean in your second question. I'm able to run blockMesh at least, but I can run the solution. Not sure if that answers your question. Maybe I'm going about this the wrong way? I just want a box with a small inlet and outlet. I tried doing that with one big block and multiple patches, but that didn't seem to work either. Thanks for the response.

May 20, 2011, 09:56		#5
murrdpirate Member Kevin Join Date: May 2011 Posts: 33 Rep Power: 14	I could have sworn that's what I did in my first attempt, and that it kept automatically placing the unpatched block faces into default, empty patches. But I must have been doing something else wrong, because what you say definitely makes sense. I'm at work at the moment, but I'll give it another shot asap. Thank you very much for your help!

May 20, 2011, 14:25		#6
murrdpirate Member Kevin Join Date: May 2011 Posts: 33 Rep Power: 14	Your first instinct was correct; the meshes were not matching on both sides of all the interior faces. I finally seem to have it working now. I think that because the meshes didn't match, the program was trying to get me to apply some boundary conditions to them. Or maybe not...I'm really not sure. Either way, thanks again for the help. This is my first non-tutorial case and I felt like I was on my last leg.