BCs in Fluent for flow inside a cylinder.
 

Good afternoon, I'm currently trying to model the reactive flow inside a closed cylindrical combustion chamber with circular/annular inlets and annular exhaust. The geometry is completely axisymmetric, and I've already done the calculations using a 2D mesh, but now I've been tasked with running the same case using a 3D mesh of a 30 degree section of the chamber.

My first question is about setting the appropriate boundary conditions: Is the axis boundary condition the correct one to use in this case? Ou would setting a symmetry BC on each of my side boundaries fix the problem? It would seem obvious to me that for a 90 degree section the symmetry condition would be okay, but not so for the smaller section I'm using.

Secondly, using the same method I followed in ICEM to model the 2D case, I created a part in the 3D model corresponding to the axis of axisymmetry of the chamber. When reading the mesh in fluent, however, this does not show up in the boundary conditions tab, where I'd like to set it as an axis (assuming this would be the right way to do so, of course!)

Any help at all would be much appreciated!