# How should I plot dv/dt in CFX?

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 December 30, 2011, 01:31 How should I plot dv/dt in CFX? #1 New Member   Ali Join Date: Dec 2011 Posts: 21 Rep Power: 8 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. Thanks, Ali Last edited by ali8500; December 30, 2011 at 01:50.

 December 30, 2011, 04:35 #2 New Member   Join Date: May 2011 Posts: 2 Rep Power: 0 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: ADDITIONAL VARIABLE: utderiv Option = Vector Algebraic Equation Vector xValue = u.Time Derivative Vector yValue = v.Time Derivative Vector zValue = w.Time Derivative END

 December 30, 2011, 04:41 #3 New Member   Ali Join Date: Dec 2011 Posts: 21 Rep Power: 8 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

 December 30, 2011, 09:57 #4 New Member   Join Date: May 2011 Posts: 2 Rep Power: 0 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. doublestrong likes this.

 December 30, 2011, 11:55 #5 Senior Member   Lance Join Date: Mar 2009 Posts: 625 Rep Power: 15 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?

 December 30, 2011, 15:47 #6 New Member   Ali Join Date: Dec 2011 Posts: 21 Rep Power: 8 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

 December 30, 2011, 17:12 #7 New Member   Ali Join Date: Dec 2011 Posts: 21 Rep Power: 8 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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