[Other] Confused about the block definition

ziming zhu · September 30, 2015, 09:45

Hello guys,
I am working on a simulation about the flow around a cylinder,and I have problems when writing the blockMeshDict .The tuition has divide the region as the follwing picture:2015-09-30 21:29:10????.jpg

Then he writes hex (5 4 9 10 24 23 28 29) (80 20 1) simpleGrading (10 1 1) and hex (16 10 9 15 35 29 28 34) (20 80 1) simpleGrading (1 10 1) in the blocks definition.
Why don't the two blocks have the same value,

the number of cells in each direction should be the same.

Any suggestion helpful.
Regards,
Ziming Zhu

cutter · November 23, 2015, 07:27

Hi!

That's right - the cell numbers need to match for neighboring block edges and faces.

The definition of blocks needs to follow a certain scheme, have a look at figure 5.5 of http://cfd.direct/openfoam/user-guide/blockmesh/. However there multiple possible/valid definitions for one single block - depending on the vertex index to start with. This induces a local coordinate system for each block.

In your case the the blocks are defined in such a way that the first local coordinate direction of the first block matches the second local coordinate direction of the second block. That's why the discretization is specified differently.

You can either live with the different definitions of the discretizations, or change the one of the blocks (which might cause same problems with other adjacent blocks).

Hope that helps.

Cutter

September 30, 2015, 09:45	Confused about the block definition	#1
ziming zhu New Member Join Date: Sep 2015 Posts: 1 Rep Power: 0	Hello guys, I am working on a simulation about the flow around a cylinder,and I have problems when writing the blockMeshDict .The tuition has divide the region as the follwing picture:2015-09-30 21:29:10????.jpg Then he writes hex (5 4 9 10 24 23 28 29) (80 20 1) simpleGrading (10 1 1) and hex (16 10 9 15 35 29 28 34) (20 80 1) simpleGrading (1 10 1) in the blocks definition. Why don't the two blocks have the same value,the number of cells in each direction should be the same. Any suggestion helpful. Regards, Ziming Zhu

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November 23, 2015, 07:27		#2
cutter Senior Member Join Date: Mar 2010 Location: Germany Posts: 154 Rep Power: 16	Hi! That's right - the cell numbers need to match for neighboring block edges and faces. The definition of blocks needs to follow a certain scheme, have a look at figure 5.5 of http://cfd.direct/openfoam/user-guide/blockmesh/. However there multiple possible/valid definitions for one single block - depending on the vertex index to start with. This induces a local coordinate system for each block. In your case the the blocks are defined in such a way that the first local coordinate direction of the first block matches the second local coordinate direction of the second block. That's why the discretization is specified differently. You can either live with the different definitions of the discretizations, or change the one of the blocks (which might cause same problems with other adjacent blocks). Hope that helps. Cutter