Learning Forum

[ag1991]

Hi,

I was wondering how to define on CFD Post right at the CEL Language Expression tab a new variable where I have two different time step case and data archives corresponding to the same geometry already loaded.

The idea is combining the values of Mean Wall Shear Stress from these two time steps to create the new variable, i.e. Wall Shear Trnavg(at time step no.2) + Wall Shear Trnavg (at time step no.2). I am not totally aware if this is possible and have no clue about the syntaxis, as far as I know, you may handle values from different zones by typing something like this : Wall Shear Trnavg()@Zone1, but combining values from two time steps is another kettle of fish.

Thank you

[DrAmine]

If this is possible but then require Perl Scripting as you want to do deep sum and not a reduced operation. The latter can be done easiy like average of variable 1 in case + average of variable 2 in case 2. I am not aware about a direct solution for your problem without the need to code.

[Rob]

If you want to average the average then it'll be quicker with a calculator as you're working with single figures. If you want to average the data field then have a look at data sampling in Fluent: note this needs switching on before running the time steps you want to average.

[ag1991]

DrAmine and Rob, well, let's forget about the Mean Wall Shear Stress as it may complicate things more than necessary. What about creating a variable where I had for instance Pressure (at time step 1) - Pressure (at time step 2)? So I could obtain the pressure differences on all regions between the two time steps? I am exclusively talking about the creation of a Expression within CFD-Post. How would you achieve that?

Thank you both

[DrAmine]

I still think you will require Perl Scripting. Better to do that in CFX or Fluent before solving. If you are using Fluent and you can access old time values. In CFX you can ask for add variable and time derivative.