[Danilo_King]

Greetings to everyone! My first post here.
I'm relatively new to OpenFOAM and I have to use it for my thesis.
I'm running multiple simple topology optimization cases from which I extract the resulting fluid domain (example in the attached image) that I need to use for further testing with a CHT solver. During the meshing the challenge is that within the boundaries of the fluid region I need the rest to be filled with the solid region cells (like making it a full block again).
So far I tried creating a blockMesh of the same size as the boundaries of the fluid region assigning it to solid

  blocks(hex (0 1 2 3 4 5 6 7) solid (100 100 36) simpleGrading (1 1 1));

and then in snappyHexMeshDict set the cellZone for my fluid domain

refinementSurfaces
    {
        solid_to_fluid
        {
            level           ( 0 0 );
            faceZone        solid_to_fluid;
            cellZone        fluid;
            mode            inside;
        }
    }

and another approach where instead of the blockMesh of the same size, I use an extra STL of the same size superimposed with my fluid domain STL.

Both methodologies give me the desired result visually with both regions separated, but I keep getting errors from paraview that the mesh is missing cells and I'm unable to proceed further, which makes me doubt the correctness of my approach so I am asking for help the almighty forum.

I also attached the snappyHexMeshDict and the blockMeshDict.

blockMeshDict.txt

snappyHexMeshDict.txt

IMG_6561.jpg