Velocity gradient

saewoong98 · October 21, 2009, 20:43

Hi everyone.
I am trying to compute the each componet of shear strain rate, mean value of each velocity gradient component, and standard deviation of each velocity gradient component. I am doing my calculations with D.N.S.
Is there anyone how to compute those variables?

stumpy · October 27, 2009, 15:54

It looks like only the scalar Shear Strain Rate is available, so I can't help you there. The other variables are easily obtained:
- Create Additional Variables in CFX-Pre for each of the required velocity gradients. Set the AV values to "Velocity u.Gradient X", "Velocity u.Gradient Y", etc. During the solution you can now access these gradients via the AV's
- Under "Output Control > Trn Stats", create the required statistics for the AV's (mean and standard deviation).

saewoong98 · October 28, 2009, 11:14

Thank you for your help.
I tried to create additional variables in CFX-pre.
I opened " Edit in command".
I typed in Option = Value, Additional Varialbe Value = Velocity u.Gradient X.
But, it didn't work.
One more question, those variables didn't show up on the Trn Stats variable list.
Can you give me any advice?

stumpy · October 29, 2009, 13:09

When you say it didn't work, what was the error. Try running in the solver, it may work and it's jsut Pre that giving an error. I'm not sure why you're typing in values through the commend editor - use the GUI!

saewoong98 · October 29, 2009, 18:09

I created 9 additional variables for each velocity gradient.
The options that I can handle are variable type, unit, tensor type.
That's why I typed in command window.
Am I doing wrong way?

October 21, 2009, 20:43	Velocity gradient	#1
saewoong98 New Member Join Date: Mar 2009 Posts: 3 Rep Power: 17	Hi everyone. I am trying to compute the each componet of shear strain rate, mean value of each velocity gradient component, and standard deviation of each velocity gradient component. I am doing my calculations with D.N.S. Is there anyone how to compute those variables?

October 28, 2009, 11:14		#3
saewoong98 New Member Join Date: Mar 2009 Posts: 3 Rep Power: 17	Thank you for your help. I tried to create additional variables in CFX-pre. I opened " Edit in command". I typed in Option = Value, Additional Varialbe Value = Velocity u.Gradient X. But, it didn't work. One more question, those variables didn't show up on the Trn Stats variable list. Can you give me any advice? Last edited by saewoong98; October 28, 2009 at 20:13.

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October 27, 2009, 15:54		#2
stumpy Senior Member Join Date: Apr 2009 Posts: 531 Rep Power: 21	It looks like only the scalar Shear Strain Rate is available, so I can't help you there. The other variables are easily obtained: - Create Additional Variables in CFX-Pre for each of the required velocity gradients. Set the AV values to "Velocity u.Gradient X", "Velocity u.Gradient Y", etc. During the solution you can now access these gradients via the AV's - Under "Output Control > Trn Stats", create the required statistics for the AV's (mean and standard deviation).

October 29, 2009, 13:09		#4
stumpy Senior Member Join Date: Apr 2009 Posts: 531 Rep Power: 21	When you say it didn't work, what was the error. Try running in the solver, it may work and it's jsut Pre that giving an error. I'm not sure why you're typing in values through the commend editor - use the GUI!

October 29, 2009, 18:09		#5
saewoong98 New Member Join Date: Mar 2009 Posts: 3 Rep Power: 17	I created 9 additional variables for each velocity gradient. The options that I can handle are variable type, unit, tensor type. That's why I typed in command window. Am I doing wrong way?