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Old   June 12, 2007, 05:12
Default CEL expression
  #1
Selim
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Hallo,

I have the option Velocity u.Gradient x in CFX 5 ,fine.

But I need also gradient of this expression?

How can I do that?

thnks Selim

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Old   June 12, 2007, 09:08
Default Re: CEL expression
  #2
opaque
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Dear Selim,

Would you mind sharing your need for a second derivative of velocity? Perhaps there are other alternatives..

The gradient of the gradient of a vector is a third order tensor, that is not available via CEL.

Opaque

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Old   June 13, 2007, 10:26
Default Re: CEL expression
  #3
Selim
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Hi opaque,

Actually I need the gradient of a scalar. Temprature,x-component of velocity etc. Is there a way to get from CFX post?

Thnks, SElim
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Old   June 13, 2007, 11:14
Default Re: CEL expression
  #4
opaque
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Dear Selim,

Check in the Variables tab for CFX-Post. If the <variable of interest>.Gradient <X/Y/Z Component> is not already listed, it is not available at all.

Gradients are usually written for variables that are used for the High Resolution/Specified Blend Factor advection schemes..Otherwise, they are not written to the results file, and consequently unavailable in CFX-Post..

You could create an Vector Algebraic Additional Variable in CFX-Pre, and set the values to the gradient components you need.. Then, this AV will be written to the results file.

ADDITIONAL VARIABLE: MyAvForTempGrad

Option = Vector Algebraic Equation

Vector xValue = Temperature.Gradient X

Vector yValue = Temperature.Gradient Y

Vector zValue = Temperature.Gradient Z

END

The above should work in ANSYS CFX 11.0, in 10.0 you must use UserFortran to access the gradients..

Hope it helps,

Opaque

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Old   June 14, 2007, 07:27
Default Re: CEL expression
  #5
Selim
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Thanks in advance,

Isnt there anyway to do it with Post? Not so easy for me to do the calculations from the begining

Regards, Selim

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Old   June 14, 2007, 09:03
Default Re: CEL expression
  #6
opaque
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Dear Selim,

If your case is steady state, you only need to restart the solver for 1 iteration.. For the transient case, do you need the gradient at all timesteps, or only at the last one? For the latter, just run an additional time step.

Hope it helps,

Opaque

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Old   June 14, 2007, 10:51
Default Re: CEL expression
  #7
Sohag
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Sorry to distrub both of you. I also want to wite a velocity gradient e.g at the wall velocity u=(delu/deln), n is the normal inword to the wall. How I can write it using CEL expressions in CFX-10.I would be very grateful to you if you give me any informations.Please help me. Sohag
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