HOW TO CREATE FLUID VOLUME FOR THIS MODEL

[OSO666]

While the solid mesh for a design part occupies the part itself, the fluid mesh occupies the void between the bodies.
Because the void itself is not a body, I must create a solid body to occupy the void.
If i import a model like the one attached, how can i create that solid volume with NX NASTRAN FLOW?

http://files.engineering.com/getfil...-472c-9b92-ab2fee058e35&file=Mixing_Valve.IGS

http://files.engineering.com/getfil...a-9c7a-724734e0f9b8&file=4-2-1_Exhaust.SLDPRT

THANKS FOR YOUR HELP