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ali8500 December 30, 2011 01:31

How should I plot dv/dt in CFX?
Hi Guys,
Does anyone know How I can plot dv/dt in CFX where v is velocity and t is time?? I want to see the change of this term at specific time for my 2d simulation. I like to have a contour showing the changes of dv/dt.


alemarins December 30, 2011 04:35

Time derivatives are partially supported in CEL.
Velocity time derivatives can be accessed with the ".Time Derivative" operator by setting up an additional variable as follows:

Option = Vector Algebraic Equation
Vector xValue = u.Time Derivative
Vector yValue = v.Time Derivative
Vector zValue = w.Time Derivative


ali8500 December 30, 2011 04:41

Thanks for your response.
What is utderiv? do I need to define a new variable named utderiv?
I've started using CFX recentley. could you please explain more about the code?
tnx :)

alemarins December 30, 2011 09:57

utderiv is the name of the vector variable with du/dt, dv/dt, and dw/dt components.

This way could be simpler for you:
1) from CFX-Pre GUI define a new Additional Variable named "utderiv" (or whatever you like)
2) in the panel select: Variable Type = Unspecified; Units [m s^-2]; Tensor Type = Vector
3) go to Domain->Fluid Models->Additional Variable Models and select "utderiv" in the selection area
4) flag the check-box just below the selection area
5) type "u.Time Derivative" in Vector xValue, and so on.

Lance December 30, 2011 11:55

huh, I had no idea you could do that.
Reading a bit in cfx_ref.pdf I also found .Magnitude, .Gradient, .Curl, .Laplacian among others. Do they also work like .Time Derivative on AVs?

ali8500 December 30, 2011 15:47

Thank you so much Alemarins.
I have two more questions. In Vector-xvalue box I have to enter u.Time Derivative or Velocity u.Time Derivative???
My second question: It seems that I have to run my simulation again so as to get the results for my new variable right? since I've already run my simulation is there any way to find du/dt in CFD-post?
Thank you for your help

ali8500 December 30, 2011 17:12

I got the answer for my first question. As you said u.Time Derivative works. I'm just curious to find a way so as to plot du/dt in CFD-post.

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