Internal flow

To fix the boundary conditions, prepare watertight STL files as inlet.stl, outlet.stl, ect. Then in system/snappyHexMeshDict.geometry define: section

geometry
{
    inlet.stl
    {
        type triSurfaceMesh;  // It grabs STL files from constant/triSurface
        name inlet;
    }
    outlet.stl
    {
        type triSurfaceMesh;
        name outlet;
    }
    wall.stl
    {
        type triSurfaceMesh;
        name wall;
    }
}

While in the refinement surfaces section you can address the info of the patch:

refinementSurfaces
{
    inlet
    {

        level (2 2);
        patchInfo
        {
            type patch;
        }
    }
    outlet
    {

        level (2 2);
        patchInfo
        {
            type patch;
        }
    }
    wall
    {
        level (2 2);
        patchInfo
        {
            type wall;
        }
    }
}