Hi Joseph, 

Going by what has been mentioned here, I would go with outflow boundary condition. You can probably try to relocate the outflow boundary condition.



Thank you for your reply Rahul. Still. my model is not consistent in shape along the vessel, which means the flow within the vessel is always in the B position in the figure you attached. To use outflow as boundary condition, I think I will need to  Therefore I don't really think outflow boundary condition does not fit my case.