I wonder if you have got your answer by now, but I give you my thoughts.nFirst of all, from your figures, figure 1 is not the result of appending figures 2 and 3 at the positions shown on figures 2 and 3. The Fairing overset has had a motion to th left and the body overset to the right, ya? nAnyway, the background mesh does not have any overlapping wall with any wall of your components individually. This is why when only one component is appended, you don't have any orphan cell. However, the fact that you see orphan cells suggests that the two component meshes produce narrow spaces between their wall when they are appended to the background. If there are not sufficient cells between walls, orphan cells are generated. n n