Learning Forum

[M.Abdelhady]

I am trying to calculate the lambda 2 criterion using the time averaged velocity field in CFD-Post. I tried to create the lambda 2 expression using the time averaged velocity variable "Velocity.Trnavg"; simply by creating "Velocity.Trnavg.Lambda 2" expression; however, it failed and gave the following message

"ERROR

The following unrecognised name was referenced: Velocity.Trnavg.Lambda 2.

"

 

Could you please let me know how to calculate the time-averaged lambda 2 criterion in CFD-Post?

 

Thanks

[DrAmine]

You make a copy of the result file. In one session you overwrite the gelocityvfield by the mean velocity field. Afterwards you make vortex core calculation. Alternative is doing the math on the mean velocity field by your self.

[M.Abdelhady]

Thank you for your reply. How to overwrite the velocity to the mean one? I tried doing that in CFD-Post, but it could not process.

 

Thanks

[DrAmine]

Are you reading Fluent or CFX results?

[M.Abdelhady]

Fluent results

 

Thanks

[DrAmine]

Then make it better in Fluent after you enable data sampling. In CFD-Post you will require some scripting (not really difficult if you know how and know Perl).

[M.Abdelhady]

Great. Two questions:

1) For CFD-Post, to do scripting, would I do that using expressions? Is there part in the CFD-Post user guide that describe scripting that I could refer to?

2) For Fluent, how to calculate the mean field lambda 2 after starting data sampling?

 

Thanks

[DrAmine]

In Post you need to sum over time the lambda field and divide over the time duration to make sampling. If you access to customer portal probably you might find a macro for that.

In Fluent you just create custom field function for lsnda and include that CFF in transient data sampling.

[M.Abdelhady]

Great, thanks

[DrAmine]

Welcome Mark's as Is Solved.