[Sebastiant94]

Hi colleagues,

Im doing a transient simulation and need the transient simulation average value to be an "output parameter" in Workbrench. I have already defined the value in a variable called Additional Variable 1.Trnavg (see image 1) and it is the correct value, but I could not define it as an output parameter. I tried to create an expression but I get an error (see image 2).

Could someone help me please? Thank you!

[ghorrocks]

Check you have got the variable types correct:

"Additional Variable 1.trnavg" is a scalar field variable. That is, it is the transient average of "Additional Variable 1" at every node in the domain.

Your CEL function just says Average2 = Additional Variable 1.trnavg so is trying to set Average2 as another scalar field variable. So this is not a single scalar value, it is a scalar variable field.

Also check your definitions of "Additional Variable 1.trnavg" and "Additional Variable 2.trnavg". One is showing it as a "x" thing and the other is showing as an arrow thing.

[Sebastiant94]

Ghorrocks thanks for your reply. I have reviewed the variable types, but when creating a variable in CFX pre, I can only select: Scalar or Vector (which is the other variable that appears with an arrow).

I created the variable because it was the only way (without the need for external programs) that I can obtain the average value of a transient simulation. Do you have any idea of having the correct variable types?

[Opaque]

x -> icon scalar variable
arrow -> icon vector variable

You cannot evaluate a field variable in the Expressions panel, only expressions that produce a "single value"

Additional Variable 1.trnavg seems to be a field variable. At which location in the domain do you want to extract a value from it?

[Sebastiant94]

Opaque thanks for your reply. Additional Variable 1.trnavg is a variable created from the instantaneous torque in a turbine rotor, the domain is the complete turbine, i created the variable in order to use the "transitory statistic"

Excuse me, I am new here, when you say: "I do not answer CFD questions by PM. CFD questions should be posted on the forum", should I re-post on this forum?
https://www.cfd-online.com/Forums/main/

Regards,

[ghorrocks]

If you intended "Additional Variable 1.trnavg" to be the instantaneous torque on a rotor I suspect you have misunderstood how this works.

torque_x/y/z()@rotor is the CEL command you are looking for (note you have to replace x/y/z with the x, y or z direction depending on torque axis you want), and if you send it to a monitor point it will plot this in Solver manager as the solver progresses.

Also, this is a basic operation in CFX. Have you done the CFX tutorials? They show how to do the basics like monitor points. You are wasting your time if you try to use the software without knowing the basics. You can get the CFX tutorials from the CFX documentation or in the ANSYS Customer webpage (or the ANSYS academic webpage if that is you).

Finally - Opaque and myself have "Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum." in our footer as we frequently get people sending Private Messages (PM) to us asking CFD questions. We do not answer CFD questions sent to us by PM, CFD questions should be posted on the forum. The forum you linked to is just the main CFD forum - that is a good place to ask general questions about CFD, such as differences between software, the fundamental equations and physics and so on.

[Sebastiant94]

Hello ghorrocks, thanks for the explanation of the forum. Regarding what you tell me about instant torque, it is not what I want. What I expect is the arithmetic average of the instantaneous torque. In image 1, you can see the instantaneous torque for 180 time steps, what I am looking for with the function is the arithmetic average of the last 90 time steps, which is the last value of the gray line. I want that value because I am doing a parametric study in the Workbrench and I want that "last" value to be displayed in the Workbrench.

Unfortunately, the only way I found for the value to come out which is correct, at least in CFXpost, is by creating a transient variable. But I was unable to use that value as an output parameter. What I don't want is to have to put the variable in CFXpost, nor to calculate it through another program and manually enter it into Workbrench, since the design points will be enough.

Do you know of a way to find the arithmetic average of the instantaneous torque for the last 90 time steps, and that this unique value will reflect in Workbrench as an output parameter?

[ghorrocks]

The way I normally do this is as I described - send it to a monitor point, export the data from Solver Manager and use something like matlab/python/excel to calculate the average or whatever function you want to do. But if you are doing a parametric study in workbench this approach is not appropriate.

I see why you have done what you done now. It is a very messy way of doing it but I cannot think of a better way. When I am back in the office next week I will see if I can find a better way to do it.

[Sebastiant94]

Thank for your collaboration Ghohrrocks and I´m waitting your answer!

[ghorrocks]

Found it

Look at the CFX-Pre users guide, section 23.1.5.1.8.8. It describes how you can do transient statistics on monitor points.

This means you can set up a simple monitor point outputting the torque using the torque_x/y/z() function, and you can use the monitor statistics options to make it a running average.

So no need for an additional variable or full domain transient averaging.

[Sebastiant94]

Hello ghorrocks,

Sorry for the delay in my reply. I have already done (see image 1)what you tell me and says in the user´s guide. For example in the attached image, I took the arithmetic average using monitor statistics for the instantaneous values from time step 90 to 180. The last value, that is the one of the time step 180, is the value that I need since it means the arithmetic average for 90 time steps. I have the difficulty when I want that value to appear in the workbrench as an output parameter, this is what I still can't get.

Therefore, what occurred to me was to determine a variable that gives me the value. The truth is I did not hide any more ideas to obtain an output parameter in Workbrench.