what is the possible problem
 

I designed a cube box as background grid, and a surface(.stl ) to slice this box.

type
blockMesh
snappyHexMesh

succeed!

and then type paraFoam

the cube box unsliced is shown in the window.

locationInMesh in snappyHexMeshDict is confirmed correct.

If I change the area of refinement parameter in snappyHexmeshDict, it does work.

Why the .stl file didn't work? what is the possible problem?

Hi,

just an idea:

The meshers blockMesh and snappyHexMesh write each intermediate mesh of the meshing process to a different time directory (0 or constant for block mesh, 1 for castellated mesh, 2 for snapped mesh and maybe 3 for mesh with boundary layers).

Assuming the meshing process succeeded, you might need to skip to the last time step in paraFoam in order to see the final mesh (button 'Last Frame' in toolbar 'VCR Controls').

You may also use 'snappyHexMesh -overwrite' in order to write all meshes into into a single time step directory.

Good Luck!