Herschel-Bulkley viscosity model

[TZiegler]

Hello,

I have a question regarding the different viscosity models implemented in Elmer.
The model I am looking for is called Herschel-Bulkley viscosity model:
http://en.wikipedia.org/wiki/Herschel–Bulkley_fluid

I could not locate it so I guess it is not implemented?
Can I contribute towards implementing it?

Cheers
Tobias

[raback]

Hi

To implement it add a new case in module file MaterialModels.src in the following function:

Code: Select all

   FUNCTION EffectiveViscosity( Viscosity,Density,Ux,Uy,Uz,Element, &
                      Nodes,n,nd,u,v,w, muder ) RESULT(mu)

It takes the base viscosity and strain rate invariant, muder, and computes with the given parameters a modifed viscosity mu. The viscosity is computed at each integration point. Just make the modification to the src file and say 'make' & 'make install' (assuming you have compiled Elmer yourself). When you've tested it, we are happy to add it to the official distro.

-Peter

[TZiegler]

Hello,

I think the Herschel-Bulkley viscosity is essentially the same as the Power-Law:
If I take the derivative of the stress in the Herschel-Bulkley model with respect
to γ (the shear rate)

τ = τ0 + Kγ^n

I get something like the Power Law Viscosity:
µ = dτ/dγ = (K*n) * γ^(n-1)

What I don´t understand is in the ElmersModelsManual p20 the formulas are the same for above
the critical shear rate and below?

Cheers
Tobias

[raback]

Hi

What I don´t understand is in the ElmersModelsManual p20 the formulas are the same for above
the critical shear rate and below?

There's a tiny difference. The suffix in the latter refers to the critical shear rate and makes the viscosity constant.

-Peter