[hand90]

Hi everyone,

I have come across a situation where I would like to monitor certain variables in a transient simulation (LES), which are not available for selection. For example I would like to monitor the "cumulative arithmetic mean of the product of pressure and temperature" (pT) and other products e.g. (uT), (vT), (wT),...

At first I thought that I could do something similar to CFD-Post, where an expression is defined, then a new variable is created based on that expression. However, I don't think this is possible or I have not figured out how to do this.

Does anyone know how I would be able to create a new variable, monitor the variable and finally have the variable available in CFD-Post?

Thank you in advance for your help.

[Opaque]

The same process

- Insert an additional variable, say MyAddVar1
- Open the domain panel for which you want to compute that variable
- Select option = Algebraic Equation
- The expression for your additional variable

Additional Variable Value = Pressure * Temperature

Repeat for each of the combination you want to compute.

For the transient arithmetic average, you
- open Output Control
- select transient results/statistics (do not recall exactly)
- select the type of statistics you would like to compute
- list the variables you want the statistics of.

You should be able to visualize them in CFD-Post at the end of the simulation.

Hope it helps,

[hand90]

Thank you very much Opaque. That is exactly what I was looking for. Didn't realise that the "Additional Variable" is thereafter defined in the domain panel.


Also you are correct in the way you have described the transient arithmetic average.
- Output control
- Trn Stats
- Output Variables List
- There you can select the newly created variable.

Many thanks

[hand90]

So the first part worked perfectly, creating new variables and then create transient statistics from them.

However, one of the problems still remains. How can I monitor the cumulative arithmetic average or even save the arithmetic average at different time steps?

I assume there is no way I can imbed the arithmetic average within the expression?

[Opaque]

Try MyAddVar1.Trnave in an expression

If you want to monitor the time average at a few points only, there is no need to compute the transient statistics.

Just create a monitor point, and probe the variable of interest at the location of interest, and activate the transient statistics of the monitor point. Summary

Monitor Point/Expression

Expression value = probe(MyAddVar)@Location of interest

MONITOR STATISTICS/Option = Arithmetic Average
...

Or, just compute them in the ANSYS CFX Solver Manager. Summary:

Open the plot for your monitor points,
Go to the Derived Variable tab, insert a new definition
Select an option , say Arithmetic Average, fill the details
Press Apply

Multiple options, I am sure one of them should work for you.

[hand90]

Thanks again! Your solution works. I was not aware that I can use the transient statistics as operators in expressions. If anyone is looking for them, they are listed under "Statistics as Variable Operators" in ANSYS help.

One a side note for future reference, there is a little typo. Use "MyAddVar1.Trnavg" instead of "MyAddVar1.Trnave".

Also, I have used the second suggestion previously which works a treat if the values are only used on a monitor point.

Doing it just in the ANSYS CFX Solver Manager is also an option for everyone who is just looking for a moving arithmetic average. I haven't figured out yet how I could use a cumulative arithmetic average in the Solver Manager.

There is another option for outputting transient statistics at intermediate result. In the Transient Results tab select the Output Variable Operators check box and choose the "Full" option. However I have not used this yet and don't fully understand which variables will be output. Just found this option as I was working on the problem.


Thank you for your great assistance Opaque!