[Opaque]

Originally Posted by Jiricbeng

Opaque, thank you for clarifying.
So, to sum it up again, how shall I understand it - I defined the variable "Pressure.Time Derivative" in Pre, then ran the solver and opened the result file in CFD Post. But for some reason this variable does not work in CFD Post.
I understood that situation to be strange and that it should work. Or, please, did I miss some step in between?

Careful, to me:
Definition = left-hand side of an expression
Reference = usage on the right-hand side of an expression

You are not defining "Pressure.Time Derivative", you are referencing it in a local expression. The local expression is evaluated by the solver as needed, correct? Can you monitor your expression in the Solver Manager?

That is the end of the referencing of the expression. Do not recall if that forces the XXX.Time Derivative to also be written to the results file. It would be nice though if it happens automatically.

[Jiricbeng]

Thank you guys.

To Glenn: I did not find any variable including .Time Derivative in any extra output variable list and I cant even push it into the list anyhow...
To Opaque: I read your post carefully several times, it makes sense, but I basically do not know what to do practically based on this :-).
Yes, I created expression called "tlakderivace" which is equal to Pressure.Time Derivative. I cannot monitor this as it is not a single valued expression but a variable.
But even if I create an expression areaAve(Pressure.Time Derivative)@rotating to have single valued expression, the monitor does not work due to error message that the monitor has invalid argument Pressure.Time Derivative.

Well, please, could you give me a more step by step guide?

[ghorrocks]

You are right, the .Time Derivative variables do not seem to be available to put in the results file.

Some options:
1) Do your calculations in the solver where those variables are available
2) Define a new additional variable, set it to a CEL function and define it as [variable].Time Derivative. Then the time derivative should be available in the results file as your additional variable. A bit messy, but I suspect it will work.

[Jiricbeng]

Heureka! Done. Big thanks to both of you.

I summarize the procedure:
CFX Pre:
- create expression called for example MyExpDPDT which is defined as Pressure.Time Derivative
- create additional variable named for example as myderpressure, which is specific, units [Pa s^-1], tensor type = scalar
- go to domain, tab Fluid Models, scroll down and tick myderpressure. Then set it to Algebraic Equation and select the expression MyExpDPDT

RUN SOLVER

CFD POST
- when clicking on expression MyExpDPDT created in Pre, it works, no error.
- create new variable referencing to the expression MyExpDPDT. You have now the spatial variable time pressure derivative at each node.

One more big thanks.