Hi
I used a demo version of ANSYS a year ago.
From memory: ANSYS create their own meshes and also set boundaries.
A good workflow was:
3D design with SALOME. Separate body for fluid and one for walls.
Fusion of fluid body and wall body.
From fusion create groups of the 3D objects.
Export all together as *.step file.
ANSYS can import *.step.
Further work according to ANSYS manual.
Small things may have slipped my mind. Please try it yourself. I have shown the red thread.