STL surface not being deleted from the back ground mesh
 

Hi there,
The title of this post gives it away a bit. I have a simple background mesh and a short cylinder in an STL format. I want to delete the cylinder from the background mesh so i can model fluid flow over this cylinder. When I use sHM, it doesn't seem to delete the volume of the cylinder but an image of the cylinder does appear on the wall of the backgroun mesh (in the correct position). Anyone have any idea's on this?
Kind Regards,
Kit

solved it for anyone having a similar problem in future, I copied the snappy hex dict from the multiregionheater tutorial, and I needed to delete a bit in the refinment surfaces:

faceZone bottomAir;
cellZone bottomAir;
zoneInside true;