How to generate the cylindric velocity components of a simple annular diffuser
 

this problem concerns a air flow motion from impeller to diffuser ring then into the volute in a centrifugal compressor. Now i'm only interested on the flow angle on the annular diffuser outlet face, so that i just extracted the domain diffuser ring from the entirety.

i know its the direct way to use turbo application with defining rotation axis. But how could i fulfill the request on hub and shroud?? its simply a annular diffuser and both upper and lower walls are stationary.

May anyone help me with that? or just any clues about another method. Will be thankful:)