define shear_stress expression directly

brucecumt · May 31, 2012, 02:31

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 don’t 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!

brucecumt · June 2, 2012, 05:15

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.

May 31, 2012, 02:31	define shear_stress expression directly	#1
brucecumt New Member bruce Join Date: May 2012 Posts: 12 Rep Power: 14	Hi all, I want to implement this model in ANSYSFLUENT: shear_stress = yield_stress + Kshear_rate. In this model, shear_stress=yield_stress when shear_rate=0. But in FLUENT, it seems that shear_stress=viscosityshear_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 don’t 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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June 2, 2012, 05:15		#2
brucecumt New Member bruce Join Date: May 2012 Posts: 12 Rep Power: 14	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.