Periodic Boundaries
 

Hi,

I am doing a preliminary mesh investigation where I want to look at the fully developed velocity profile in a 19 mm pipe. I want to make cyclic boundaries so I have no change in velocity profile along the pipe length.

I am using CFX mesh Generator (unstrusctured mesh) and apply a periodic Domain Interface between the in- and outlet. Also I specify a velocity in the pipe direction under "Global initial Conditions".

I have problems getting the solution to converge and when looking at the results in post-processing the velocity is changing along the pipe!

I am using ANSYS workbench v 10.0..

Can anyone help me with this?

Re: Periodic Boundaries
 

Hi Christina,

you need to include a momentum source in the flow direction for the whole domain which balances the pressure drop in the pipe. If you know what your pressure drop per unit length is, you can calculate the source easily; if you only know the flow rate, then you will need to use trial and error to get the correct value.

In Release 11.0, these types of problems can be set up more easily using new models for Domain Interfaces.

Regards,

Johnson

Re: Periodic Boundaries
 

Hi Johnson,

Thanks for your quick reply but I still have some problems including the proposed momentum source. In CFX PRE I can only make a source point which can not fix the problem…

I guess my question is: How do I include a momentum source in the flow direction??

Thanks in advance Christina

Re: Periodic Boundaries
 

Hi Christina,

You have to define a Subdomain over your Domain, here you can include all the momentum sources you want.

Fusion