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define shear_stress expression directly

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Old   May 31, 2012, 01:31
Question define shear_stress expression directly
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Hi all,
I want to implement this model in ANSYSFLUENT: shear_stress = yield_stress + K*shear_rate. In this model, shear_stress=yield_stress when shear_rate=0.
But in FLUENT, it seems that shear_stress=viscosity*shear_rate for both Newton and Non-Newton fluids which means shear_stress will become 0 when shear_rate is 0.
I know we can define viscosity to implement this model for shear_rate>0. However, I donít know how to make shear_stress=yield_stress when shear_rate=0.
I wonder whether we can implement the shear_stress expression as follows by defining shear_stress directly with the help of UDF in FLUENT.
shear_stress = yield_stress + K*shear_rate.(shear_rate>=0)
Anyhelp will be appreciated!
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Old   June 2, 2012, 04:15
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I guess in ANSYSFLUENT it is always the case that shear stress will become zero when shear rate is zero as we cannot change the model in FLUENT that shear_stress=viscosity*shear_rate.
Any suggestion is highly appreciated.
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bingham, define shear stress, udf

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