[guest1104]

I have a larger body (fluid domain) within which there are couple other smaller bodies that I want to use as subdomains. But when I import the mesh, the domain in CFX-pre has multiple assemblies in location. This is resulting in the solver running into an error- "3 isolated fluid regions were found in domain Domain 1".

Can someone help me sort it out?

[Gert-Jan]

You should put all volumes in the main domain and on top of that define subdomains for the smaller bodies.
This should work fine unless your volumes are not connected properly and don't have a conformal mesh. But that is impossible to judge without more information. You should share more info (pictures!) on your geometry, how is was created, meshed, imported, etc.