Tube can also be model as 2D axisymmetric, this also help to reduce computational time.

Periodic boundary conditions are used when the flows across two opposite planes in your computational model are identical.

For more details on periodic boundary condition, please refer user's guide: 7.4. Boundary Conditions (

If you are not able to access the link, please refer to this forum discussion: Using Help with links (

Please have a look at the video on periodic boundary condition:

Hope you find this useful.

Thank you