[Ram]

Hi,

How to make a transition in Hexa mesh from fine to coarse?

Example: A common edge would have 12 elements one side and 8 elements on other side.

[Gert-Jan]

try the tutorials.

[Ram]

To be more precise....I have two 3D blocks to be merged. One of the parallel edge on the interface has 40 and 20 elements. Now when I merge both, I need a transition between both blocks and require only hexa elements.

[Gert-Jan]

You cannot do this. 40 and 20 simply don't match. You either need to increase one or decrease the other. Alternatively:
- you need a block coming from the side. But this is too difficult to explain in words. You need to share pictures.
- create an interface in the cfd package that you use.

[bluebase]

Hi Ram,

as Gert-Jan said, the blocking structure always has to have the same number of nodes between neighbouring blocks.

If your solver can deal with hanging nodes, than you might consider using refinement levels with will increase the number of elements in a block by a given factor. However, in the underlying blocking structure still has the explained interdependency.

Another option are interface boundaries. In a lot of cfd solvers such interfaces do not need to be conformal. One might consider hanging nodes as a special case of interfaces.

Finally, if you really cannot workout how to get the desired mesh density you can try a technique called nesting:
nesting.jpg
Here you create c-grid on one side of the "interface". However, this comes at the cost of somewhat misaligned elements (element faces should be aligned with the flow to reduce numeric diffusion). Moreover, you mostly have to create these structures manually.
An additionally nice feature might be the possibility fully resolve to 1-to-3 ratios of refinement levels with this nesting strategy (There is some info spread in this forum). However, the automatic nesting in this case creates tiny nestings for each original element layers... Again this might lead to undesired numerical diffusion.

Best regards,
Sebastian