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Old   September 16, 2010, 03:24
Default turbulence model
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Ali Jafarizade
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hi
are the turbulence models that used for newtoninan fluid diffrent from non-newtonian fluid in fluent? how about in general?
thanks in advance
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Old   September 21, 2010, 16:57
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I asked ANSYS tech support, whose response is below.

The turbulence models for use with non-Newtonian fluids are the same as those for newtonian fluids. Newtonian fluids are implemented by changing the viscosity dependency for the fluid material; the other selections stay the same.

I do not quite understand so I'm asking for clarification. However, I thought I'd go ahead and respond with the information thus far.

Last edited by Jade M; September 23, 2010 at 12:55.
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Old   September 22, 2010, 04:07
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Hamid Zoka
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I am not sure about it.
what about bossinesque approxiamtion?
how is turbulence viscosity in non-newtonian fluids defined?
turbulence characteristics of newtonian fluids seems to be different than newtonains.
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Old   September 23, 2010, 12:40
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I am not quite satisfied with the response either. When I asked for elaboration, tech support responded

I meant that all the turbulence models we have support non-newtonian fluids. The implementation of non-newtonian viscosity is similar to making property change to the fluid. The Non-Newtonian model just allows viscosity to depend on Shear stress and other variables.

I also submitted a new service request to see the response from another person, who stated

With non-Newtonian models we generally alter only the dynamic viscosity term, other terms are calculated in the same fashion.

I still do not completely understand but this is all the time that I have to devote to this issue at the moment.

From the CFX documentation, it looks like built-in non-Newtonian dynamic viscosity models are new in Release 12, which is probably a great improvement. However, I do not see anything in reference to turbulence modelling. I spent a great deal of time understanding turbulence modelling earlier this year and did not see anything in reference to non-Newtonian fluids in the CFX documentation. I am not sure as to a good source to refer you to. If you have access to ANSYS tech support, I would suggest directing questions to them.

Good luck!
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Old   September 25, 2010, 01:34
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I agree with Hamid. The Boussineq approximation does not hold for non-newtonian fluids and the definition of turbulent viscosity has to be modified. There was a study on the addition of polymer particles in blood a while ago (2002 maybe) and they found that the flow became turbulent at Re ~ 100.

You can trying using the Reynolds stress models (provided the numerical computations remain stable). Another option might be to check the documentation of OpenFOAM online. The implementation of a non newtonian turbulence model might be similar in Fluent and OpenFOAM.

Good luck,
Harish
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