Learning Forum

[Lu Mneg]

I am writing a UDF for Fluent, and I need to access the values of flow variables on the boundary faces at the previous time step. For cell variables at the previous time step, I can access them using the C_U_M1(c,t) macro. Is there a similar data access macro available for accessing the variables on the boundary  faces at the previous time step? Or is there an alternative way to access this data?

[Rob]

Possibly, try using F_ in place of C_ and see if it works. You'll get an error if it's not available, so save first in the event it's a Task Manager job to close Fluent. 

There are other options, but as they're not documented I can't comment on a public forum. 

[Lu Mneg]

 

Thank you for your response. Can you send other methods to my personal email? 

 

[Lu Mneg]

[Rob]

I can't, Ansys staff must comply with US Export Law, so everything is posted here and only public responses. Commercial clients are checked so support is both private and at a higher level. 

I'll remove the email address to prevent spam/unwanted messages. 

[Lu Mneg]

Unfortunately, when I replace F_ with C_, Fluent will output 'The fl process could not be started.

[Rob]

Which means it's probably not available. Do you need the boundary value, or is the adjacent cell value sufficient? 

[Lu Mneg]

Yes, I need boundary values in order to calculate the time rate of change of velocity （∂u/∂t）at the boundary. Using the adjacent cell value would lead to non-conservation of mass.

[Rob]

Will it change that much from cell centre to outlet? You might be able to mess with EXECUTE_AT_END functions, but I really can't expand on that comment, other than to suggest some manual reading.