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shear rate and strain rate

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Old   April 16, 2014, 02:51
Default shear rate and strain rate
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Dear all,

I still don't really understand why strain rate and shear rate seem to be equal in fluent!
I wrote a viscosity udf at which the viscosity is dependent on the shear rate (this is what the original publication says, but I also found some publications using this model who are calling it "strain rate").
I also read the following thread

in which a quotation of the Fluent manual can be found
"Strain Rate (in the Derivatives... category) relates shear stress to the viscosity. Also called the shear rate ( in Equation 8.4-17), the strain rate is related to the second invariant of the rate-of-deformation tensor . Its unit quantity is time-inverse. In 3D Cartesian coordinates, the strain rate,, is defined as Eq. (30.4-30)"

which means: shear rate= strain rate

I also couldn't find any Macro concerning the shear rate, that's why I used C_STRAIN_RATE_MAG.
But I don't really understand whether this is right or wrong? Why is the shear rate equal to the strain rate in Fluent?

It would be really nice, if somebody could help me!
Thank you in advance!
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Old   August 29, 2014, 00:46
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Sangwoo Kim
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I'm sorry for posting here..
I'm also confused about it.
Clearly Fluent User Guide says that strain rate is equal to shear rate,
but why??

Anyone has an idea??

Thank you.
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