Can anyone tell me is there any online gambit tutorials which include how to set BCs for multiple zones. Especially gambit tutorial for Fluent tutorial 15 (2D Centrifugal Blower)? I would appreciate any help........

I dont't know any tutorials to that. But what is the problem? Just take the face or the volume in Zones --> Specify Continiuum Types and define I a Fluid zones. The rest of the geometry is defined as deault fluid zone when you export your mesh to fluent.