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Power law coeffs

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Old   November 4, 2014, 17:26
Default Power law coeffs
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vitor spadeto
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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
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Old   November 5, 2014, 08:19
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Please, someone? It is important for my project. Thanks!
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Old   November 6, 2014, 02:16
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Quote:
Originally Posted by vitorspadetoventurin View Post
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
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Old   November 8, 2014, 18:22
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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
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Old   November 8, 2014, 19:45
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Nara Shikamaru
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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 nu<nu_min, nu = nu_min and if nu>nu_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.
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Old   November 8, 2014, 22:13
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Dear shikamaru, my reference:

http://www.comsol.se/papers/6540/download/Fodor.pdf

thanks!
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