can i have two blockmesh blocks one inside each other
 

i'm finding difficult to capture geometry such as a thin wing for SHM without creating a huge number of cells which crashes SHM.
i want to intersect the STL with the minimum amount of cells and for that i want to create a finer block around the STl and a coarser block around it.
Can I do that with only two blocks, one inside each other?

I would probably do that in snappyHexMesh rather than in blockMesh.

I have a refinement box defined in SHM

but the stl has to intersect the blocks in blockmesh otherwise it doesn't get captured, right?
so a thin wing, even if it intersects spanwise and chordwise, if it doesn't intersect thicknesswise it won't show up?

Sorry, I haven't quite understood what you mean… Do you want to refine the mesh on the domain or on the surface of your geometry?

what i want is to use blockmesh to make a finer block where the object is to ensure intersection and a coarser block for the whole domain. ideally with just two blocks.

So you need something like what depicted in the attached image.

The domain is a simple square block from blockMesh.

The refinement zones are two blocks from SHM.

but what if you replace the sphere with an airfoil whose thickness is less than the height of a BM block?

mmm… could you post a picture that shows your blockmesh and your airfoil within it?

thanks lore. i think my mesh is pretty coarse actually. i'll try another approach for airfoils, namely a fine 2d mesh with further refinement around the surface. that should give me the resolution i need without the resource drain.