Mesh of a cylinder with different top/bottom faces
 

Hi, I'm trying to model the inside of an ionic thrust chamber which consists of a solid cylinder with different bottom and top faces:
- The bottom face has a circle in the middle (mass-flow inlet) (fig 1)
- The top face has multiple circles arranged in circular patterns (outlet) (fig 2)

My desire is to generate a fully structured mesh, but the best I could do was to generate a hex-core mesh with terrible quality tet-cells at the boundaries. Any ideas on how to tackle this problem?