# velocity gradient issue in cfx

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 November 2, 2009, 06:01 velocity gradient issue in cfx #1 New Member   harry Join Date: May 2009 Posts: 29 Rep Power: 10 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~!

 November 28, 2010, 01:02 #2 Senior Member   ali Join Date: Oct 2009 Posts: 287 Rep Power: 11 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 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 13,985 Rep Power: 107 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 Senior Member   ali Join Date: Oct 2009 Posts: 287 Rep Power: 11 I found it in documentations Thank you ghorrock

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