CFD Online Discussion Forums

CFD Online Discussion Forums (
-   CFX (
-   -   Solving Additional Variable in CFX? (

Tuks November 17, 2005 08:44

Solving Additional Variable in CFX?
Hi all, I want to solve equations for three variables(P1, P2, P3) as additional variables. The equation for the variable variation with time is,

DPi/Dt = (Nitotal-Gtotal*Piavg)/Vg for i=1,2,3 ----(a)


Piavg = volumeAve(Pi)@Domain1 AND Vg=constant.

Nitotal = volumeInt(Ni)@Domain1 AND Ni=K*(C - Piavg)

Gtot = N1total + N2total + N3total.

Is it possible to solve above equations (a)?

Rightnow i am solving additional variable by Diffisive transport equation. with Diffisivity = 1E-10 m^2/s. and Source = RHS of eq(a).

Can we use volmeAve and volumeInt over Domain in CEL?

when i tried in CFX-10.0-Pre i got following error. "The function 'volumeAve' referenced in parameter 'Source' in object '/FLOW/DOMAIN:Domain1/SUBDOMAIN:subreact/SOURCES/EQUATION SOURCE:SourceP2' has an invalid argument, 'N2total'. Only arguments that consist of a single variable name are supported by the solver."

What is this error?

NOTE: I am using the variable composition mixture in Domain1

Thank you in advance.

Regards Tuks

Rui November 17, 2005 10:34

Re: Solving Additional Variable in CFX?

Yes, you can use volumeAve and volumeInt in CEL.

About the error, try this: create an additional variable (algebraic equation) for each Ni



Rui November 17, 2005 13:09

Re: Solving Additional Variable in CFX?
Take a look at the Documentation; Reference Material; CFX Expression Language; CEL Variables, Functions and Constants; CEL Functions; Additional CFX-Solver CEL Functions; variable (page 47 in CFX-5.7.1 Documentation)

Tuks November 17, 2005 15:15

Re: Solving Additional Variable in CFX?
Hi Rui,

Thanks you for suggestions, it really helped a lot. I defined the each Ni as Additional Variable (algebraic equations). It works well. The documentation suggested also helped.

Now i could solve the equations. Yet to check validation with known values, but atleast solution has started quite well.

Thank you again



Tuks November 18, 2005 01:51

Re: Which one is right?
Hi all,

I am solving the reactions in single phase, the fluid in Domain is VARIABLE COMPOSITION MIXTURE (userMix). If additional variables are defined and we want to use those in CEL expressions then how we write those in expressions? Example, If N1 is additional variable.

a1 = volmueAve(N1)@Domain1 OR a1 = volumeAve(userMix.N1)@Domain1.

Which one is right? Because both are NOT giving any ERROR in Pre but in Post it says 'userMix.N1' doesnot exist?

Thanks in advance



opaque November 18, 2005 10:33

Re: Which one is right?
Dear Tuks,

For the ANSYS CFX solver both are correct; however, CFX-Post only understands what it is available in the results file. For your case (single phase I assume) only N1, and/or N1.Volumetric/Specific are available in the results file.

If you want to use the same set of expressions in the CFX-Solver and CFX-Post, you must stick to the common syntax. That is, phase name prefixing is not needed for single phase flows since the phase name is implied.

Good luck,


Tuks November 18, 2005 12:40

Re: Which one is right?
Hi Opaque,

Thank you for your sugesstions.

Regards Tuks

All times are GMT -4. The time now is 18:44.