Help! How to change wall to interior???
 

Dear guys,

I have a problem with meshing a cylindrical combustor which consists of a smaller diameter pipe connected by a sudden expansion to a bigger diameter cylinder. The geometry represents a premixed flow cylindrical section with center body ends with a larger diameter combustor. I meshed it using the sweep method in Ansys mesher by dividing the geometry to four quarters in the spanwise direction and sweep from every internal face to its opposite in each quarter. Because i wanted to inflate some layers (especially the shear layer down stream the center body) i divided the combustor cylinder into several cylinders inside each other to get internal fluid surfaces to be inflated. This works well in meshing but i was surprised that fluent treats these inner fluid surfaces as walls. i need to tell fluent that they are not walls they are part of fluid interior. i cannot collect the fluid bodies into one part in design modeler as this makes the mesher refuses to do inflation because the faces are over constrained! can any one help me fix this problem??