How should I plot dv/dt in CFX?

ali8500 · December 30, 2011, 00:31

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

alemarins · December 30, 2011, 03:35

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:

ADDITIONAL VARIABLE: utderiv
Option = Vector Algebraic Equation
Vector xValue = u.Time Derivative
Vector yValue = v.Time Derivative
Vector zValue = w.Time Derivative
END

ali8500 · December 30, 2011, 03:41

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, 08:57

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, 10:55

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, 14:47

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, 16:12

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.

December 30, 2011, 00:31	How should I plot dv/dt in CFX?	#1
ali8500 New Member Ali Join Date: Dec 2011 Posts: 21 Rep Power: 14	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 00:50.

December 30, 2011, 03:35		#2
alemarins 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 Saeef likes this.

December 30, 2011, 08:57		#4
alemarins 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 and Saeef like this.

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December 30, 2011, 03:41		#3
ali8500 New Member Ali Join Date: Dec 2011 Posts: 21 Rep Power: 14	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, 10:55		#5
Lance Senior Member Lance Join Date: Mar 2009 Posts: 669 Rep Power: 22	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, 14:47		#6
ali8500 New Member Ali Join Date: Dec 2011 Posts: 21 Rep Power: 14	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, 16:12		#7
ali8500 New Member Ali Join Date: Dec 2011 Posts: 21 Rep Power: 14	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.