# Power law coeffs

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 November 4, 2014, 17:26 Power law coeffs #1 Member   vitor spadeto Join Date: Nov 2014 Posts: 51 Rep Power: 5 I am simulating a non-newtonian flow, I know that openfoam can simulate with Power law model. But how can I define powerlaw coeffs on the transport properties file? Just have coeffs to crosspowerlaw and Carreau model.. Code: ```transportModel Newtonian; nu nu [ 0 2 -1 0 0 0 0 ] 1e-05; CrossPowerLawCoeffs { nu0 nu0 [ 0 2 -1 0 0 0 0 ] 1e-06; nuInf nuInf [ 0 2 -1 0 0 0 0 ] 1e-06; m m [ 0 0 1 0 0 0 0 ] 1; n n [ 0 0 0 0 0 0 0 ] 1; } BirdCarreauCoeffs { nu0 nu0 [ 0 2 -1 0 0 0 0 ] 1e-06; nuInf nuInf [ 0 2 -1 0 0 0 0 ] 1e-06; k k [ 0 0 1 0 0 0 0 ] 0; n n [ 0 0 0 0 0 0 0 ] 1; }``` thanks

 November 5, 2014, 08:19 #2 Member   vitor spadeto Join Date: Nov 2014 Posts: 51 Rep Power: 5 Please, someone? It is important for my project. Thanks!

November 6, 2014, 02:16
#3
Senior Member

Kyle Mooney
Join Date: Jul 2009
Location: Amherst, MA USA - San Diego, CA USA
Posts: 321
Rep Power: 11
Quote:
 Originally Posted by vitorspadetoventurin I am simulating a non-newtonian flow, I know that openfoam can simulate with Power law model. But how can I define powerlaw coeffs on the transport properties file? Just have coeffs to crosspowerlaw and Carreau model.. Code: ```transportModel Newtonian; nu nu [ 0 2 -1 0 0 0 0 ] 1e-05; CrossPowerLawCoeffs { nu0 nu0 [ 0 2 -1 0 0 0 0 ] 1e-06; nuInf nuInf [ 0 2 -1 0 0 0 0 ] 1e-06; m m [ 0 0 1 0 0 0 0 ] 1; n n [ 0 0 0 0 0 0 0 ] 1; } BirdCarreauCoeffs { nu0 nu0 [ 0 2 -1 0 0 0 0 ] 1e-06; nuInf nuInf [ 0 2 -1 0 0 0 0 ] 1e-06; k k [ 0 0 1 0 0 0 0 ] 0; n n [ 0 0 0 0 0 0 0 ] 1; }``` thanks

Hi Vitor,

You can set a power law fluid in a manner similar to this:

Code:
```transportModel  powerLaw;

powerLawCoeffs
{
nuMax             nuMax [ 0 2 -1 0 0 0 0 ] 1e-04;
nuMin           nuMin [ 0 2 -1 0 0 0 0 ] 1e-06;
k               k [ 0 0 1 0 0 0 0 ] 1;
n               n [ 0 0 0 0 0 0 0 ] 1;
}```
I might be wrong about the dimensions on this.

Cheers,
Kyle

 November 8, 2014, 18:22 #4 Member   vitor spadeto Join Date: Nov 2014 Posts: 51 Rep Power: 5 thanks kmooney, but I have a question.... I paper show me the power law definition: http://postimg.org/image/54gbo0nf3/ But what would be the nuMin and nuMax? I did not undertand..... Thank you, If I get success, I will post my results (validation) Best Regards, Vitor Spadeto

 November 8, 2014, 19:45 #5 New Member   Nara Shikamaru Join Date: Apr 2012 Posts: 22 Rep Power: 7 nuMin and nuMax are values that limit the viscosity in case the value for viscosity calculated by the power law equation gives something that may cause an instability. if nunu_max, nu = nu_max This is common to all power-law implementation I have seen in commercial CFD softwares. If you know the limit of your shear rate, then you can calculate them. Otherwise, I guess you take an educated guess (I am sure there is a better way). Could you please share the reference you posted picture of? Regards. Last edited by shikamaru; November 9, 2014 at 01:32.

 November 8, 2014, 22:13 #6 Member   vitor spadeto Join Date: Nov 2014 Posts: 51 Rep Power: 5 Dear shikamaru, my reference: http://www.comsol.se/papers/6540/download/Fodor.pdf thanks! shikamaru likes this.

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