CFD Online Discussion Forums - [blockMesh] 3d mesh for a pipe

Hi. I build a 3D mesh to model a pipe with a injector in the center at the inlet. The orifice of the injector is much smaller than the pipe. I decompose the whole pipe into 8 wedge blocks(45 degree each) and mesh them in the same pattern. The desired mesh is of one layer of prism cells surrounding the centerline, followed by hexahedron cells.

While meshing the 45 degree arch, I notice that if I define many grid points, say 9 for 5 degree each, the mesh generated goes completely wrong. It also includes wedge cells and checkMesh complains about shared edges, skewness, almost every thing. But when I reduce the grid points to 1 or 2, the mesh is correct.

My question is:
1.In this case, does it mean only 1 or 2 cells is allowed for the degenerated edge/the arch? If so, should I decompose the pipe into more wedge blocks with smaller angle to get it right? Then 72 blocks are needed to get 5 degree angle. It seems too much for writing the mesh file.
2 Quite probably my approach is wrong in the first place. If 2d axis-symmetric modelling is not an option, please give me some suggestions on this.

Thanks a lot!

Bei