velocity gradient issue in cfx

rystokes · November 2, 2009, 06:01

HI,

I'm trying to study shear rate in a simulation by generating the velocity gradient value in cfx. This value should have a dimension of inverse second. However, when I plot the magnitude of velocity gradient , I didn't find any unit there. So what's the definition of the variable "velocity gradient " in cfx?

Another question is about a variable， taking "velocity u. gradient" as an example, is it defined this way please?

velocity u. gradient=sqrt[(partial u/partial x)^2+(partial u/partial y)^2+(partial u/partial z)^2]?

Thanks a lot for your help in advance~!

alinik · November 28, 2010, 01:02

Hi

Did you find out about the definition of Velocity u.Gradient x in cfx?
I almost have the same problem.
There is one more thing, how can I define (partial u)/(partial x) in CEL expressions? do you have any idea?

ghorrocks · November 28, 2010, 18:21

But the variable velocity u.gradient does have units of s^-1, as expected.

And yes, velocity u.gradient=sqrt(velocity u.gradient X^2+velocity u.gradient Y^2+velocity u.gradient Z^2).

Ali's question is quite different. Read the documentation about getting spatial derivatives of variables. There is built in functions to calculate this in CEL.

alinik · November 29, 2010, 01:43

I found it in documentations
Thank you ghorrock

November 2, 2009, 06:01	velocity gradient issue in cfx	#1
rystokes New Member harry Join Date: May 2009 Posts: 29 Rep Power: 17	HI, I'm trying to study shear rate in a simulation by generating the velocity gradient value in cfx. This value should have a dimension of inverse second. However, when I plot the magnitude of velocity gradient , I didn't find any unit there. So what's the definition of the variable "velocity gradient " in cfx? Another question is about a variable， taking "velocity u. gradient" as an example, is it defined this way please? velocity u. gradient=sqrt[(partial u/partial x)^2+(partial u/partial y)^2+(partial u/partial z)^2]? Thanks a lot for your help in advance~!

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November 28, 2010, 01:02		#2
alinik Senior Member ali Join Date: Oct 2009 Posts: 318 Rep Power: 18	Hi Did you find out about the definition of Velocity u.Gradient x in cfx? I almost have the same problem. There is one more thing, how can I define (partial u)/(partial x) in CEL expressions? do you have any idea?

November 28, 2010, 18:21		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	But the variable velocity u.gradient does have units of s^-1, as expected. And yes, velocity u.gradient=sqrt(velocity u.gradient X^2+velocity u.gradient Y^2+velocity u.gradient Z^2). Ali's question is quite different. Read the documentation about getting spatial derivatives of variables. There is built in functions to calculate this in CEL.

November 29, 2010, 01:43		#4
alinik Senior Member ali Join Date: Oct 2009 Posts: 318 Rep Power: 18	I found it in documentations Thank you ghorrock