Ansys CFX Version 13 - Variable "Mass Fraction" disappeared in Pre!?!

monkey1 · July 22, 2011, 08:09

Hi!
I just tried to set up a new .def file for the simulation of gas dispersion. As a very important Value for Monitoring (and eventually Post processing, although I haven't reached the point of having a .res file yet) I need the Mass Concentraion of a substance. In Version 12.1 it was possible to select this variable to be monitored or written in a TrnResults File. Now that we switched to version 13 there suddenly is no "Mass Concentration" Variable anymore. Does anyone know if this was made on purpose by ANSYS, or if there is smth. wrong with my Installation?

Thx in advance.

ghorrocks · July 22, 2011, 08:26

They have probably just changed its name - have a look in the available variables in CFD-Post to see what they changed it to.

Isn't it a mass fraction you are looking for?

monkey1 · July 22, 2011, 08:32

First of all thx for the answer.

No it is not a mass fraction I'm looking for...at least I think so. The Mass fraction is dimensionless whereas the Mass Concentration has similar units to a density [kg/m^3]. From this value I can calculate the actual concentration in [ppm].

Looking at the proposed Variables in pre makes me think that they suppressed all "concentration" Variables. The only ones Left going in a similar direction are the density, mass fraction and the specific volume of the substance.

and as I created the whole project with the v13 it is unfortunately not possible to open it in v12.1

ghorrocks · July 22, 2011, 08:52

It probably has been renamed to something else.

But regardless, you can calculate it with mass fraction * mixture density. Either write this to a monitor point or define a user variable with this expression and you can see it in post processing.

monkey1 · July 22, 2011, 08:53

Cool.
Thanks, gonna try this. Sounds like it will do it.

Thank you.

monkey1 · July 22, 2011, 10:53

Just talked to the support. It seems to be a bug of v13.

First a lot of variables DO NOT appear in the variable selector for the output control for Results, trnResults, trnStats. BUT for Monitor they suddenly are all back.

So the support just told me: if you are missing a Variable in the output control that is supposed to be there but is some kind of "invisible" (just compare with the variables list for monitor points to know which variables are supposed to exist) then you have to perform a RIGHT KLICK in the Outline tree on Output Control.
Then select "Edit in Command Editor" and Edit manually the file.
So for example if you want to add "substancename.Mass Concentration" as a Variable for trnResults (for all those who just want to save a selected set of variables) and it offers you only "substancename.Mass Fraction" just create a trnResults file with a variable selection with e.g. Mass Fraction. In the command Editor you will read:

TRANSIENT RESULTS: Transient Results 1 File Compression Level = Default
Include Mesh = No
Option = Selected Variables
Output Variables List = r134a.Mass Fraction
OUTPUT FREQUENCY: Option = Time Interval
Time Interval = 1. [s]
END

Then you can just replace "Mass Fraction" by any suitable and existing Variable Name. e.g.

TRANSIENT RESULTS: Transient Results 1
File Compression Level = Default
Include Mesh = No
Option = Selected Variables
Output Variables List = r134a.Mass Concentration
OUTPUT FREQUENCY:
Option = Time Interval
Time Interval = 1. [s]
END

If you are not sure how the Variable is named, choose it as Monitor and copy and paste the name displayed in the command editor under "Monitor Point".

As a last remark. After this action the CFX Pre will definitly be complaining about the fact that the required variables do not exist. According to the support just ignore these warnings, create your .def file and the solve is supposed to have no Problem.

I hope this might help.

July 22, 2011, 08:09	Ansys CFX Version 13 - Variables missing/disappeared in Pre!?!	#1
monkey1 Senior Member Join Date: Jul 2011 Location: Berlin, Germany Posts: 173 Rep Power: 15	Hi! I just tried to set up a new .def file for the simulation of gas dispersion. As a very important Value for Monitoring (and eventually Post processing, although I haven't reached the point of having a .res file yet) I need the Mass Concentraion of a substance. In Version 12.1 it was possible to select this variable to be monitored or written in a TrnResults File. Now that we switched to version 13 there suddenly is no "Mass Concentration" Variable anymore. Does anyone know if this was made on purpose by ANSYS, or if there is smth. wrong with my Installation? Thx in advance. Last edited by monkey1; July 22, 2011 at 10:56. Reason: Changed the Title in Order to make it more general, as the solution showed that this seems to be a general problem of v13.

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July 22, 2011, 08:26		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	They have probably just changed its name - have a look in the available variables in CFD-Post to see what they changed it to. Isn't it a mass fraction you are looking for?

July 22, 2011, 08:32		#3
monkey1 Senior Member Join Date: Jul 2011 Location: Berlin, Germany Posts: 173 Rep Power: 15	First of all thx for the answer. No it is not a mass fraction I'm looking for...at least I think so. The Mass fraction is dimensionless whereas the Mass Concentration has similar units to a density [kg/m^3]. From this value I can calculate the actual concentration in [ppm]. Looking at the proposed Variables in pre makes me think that they suppressed all "concentration" Variables. The only ones Left going in a similar direction are the density, mass fraction and the specific volume of the substance. and as I created the whole project with the v13 it is unfortunately not possible to open it in v12.1

July 22, 2011, 08:52		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	It probably has been renamed to something else. But regardless, you can calculate it with mass fraction * mixture density. Either write this to a monitor point or define a user variable with this expression and you can see it in post processing.

July 22, 2011, 08:53		#5
monkey1 Senior Member Join Date: Jul 2011 Location: Berlin, Germany Posts: 173 Rep Power: 15	Cool. Thanks, gonna try this. Sounds like it will do it. Thank you.

July 22, 2011, 10:53		#6
monkey1 Senior Member Join Date: Jul 2011 Location: Berlin, Germany Posts: 173 Rep Power: 15	Just talked to the support. It seems to be a bug of v13. First a lot of variables DO NOT appear in the variable selector for the output control for Results, trnResults, trnStats. BUT for Monitor they suddenly are all back. So the support just told me: if you are missing a Variable in the output control that is supposed to be there but is some kind of "invisible" (just compare with the variables list for monitor points to know which variables are supposed to exist) then you have to perform a RIGHT KLICK in the Outline tree on Output Control. Then select "Edit in Command Editor" and Edit manually the file. So for example if you want to add "substancename.Mass Concentration" as a Variable for trnResults (for all those who just want to save a selected set of variables) and it offers you only "substancename.Mass Fraction" just create a trnResults file with a variable selection with e.g. Mass Fraction. In the command Editor you will read: TRANSIENT RESULTS: Transient Results 1 File Compression Level = Default Include Mesh = No Option = Selected Variables Output Variables List = r134a.Mass Fraction OUTPUT FREQUENCY: Option = Time Interval Time Interval = 1. [s] END Then you can just replace "Mass Fraction" by any suitable and existing Variable Name. e.g. TRANSIENT RESULTS: Transient Results 1 File Compression Level = Default Include Mesh = No Option = Selected Variables Output Variables List = r134a.Mass Concentration OUTPUT FREQUENCY: Option = Time Interval Time Interval = 1. [s] END If you are not sure how the Variable is named, choose it as Monitor and copy and paste the name displayed in the command editor under "Monitor Point". As a last remark. After this action the CFX Pre will definitly be complaining about the fact that the required variables do not exist. According to the support just ignore these warnings, create your .def file and the solve is supposed to have no Problem. I hope this might help.