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nonNewtonianIcoFoam, wired nu

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Old   March 10, 2013, 23:19
Default nonNewtonianIcoFoam, wired nu
  #1
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Dongyue Li
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Hi FOAMERS,
I want to testify a simple case to try nonnowtonian fluid.
transport dic is this:
Code:
transportModel  CrossPowerLaw;

CrossPowerLawCoeffs
{
    nu0             nu0 [ 0 2 -1 0 0 0 0 ] 5e-5;
    nuInf           nuInf [ 0 2 -1 0 0 0 0 ] 5e-2;
    m               m [ 0 0 1 0 0 0 0 ] 20;
    n               n [ 0 0 0 0 0 0 0 ] 0.2;
}
Its a kind of shear thinning fluid.

But I got the result is like this:

I think the nu in the bottom cornor should be big,but its not. Whats the problem?

Thanks in advance.

just run nonNewtonianIcoFoam



This problem has been handled. nu0 and nuInf is contrary.

Another issue:

What is m? is it consistency index? But the dimension is s which is different with pa.s^n.
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Last edited by sharonyue; March 11, 2013 at 04:40.
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Old   March 12, 2013, 09:06
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Dongyue Li
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Does anyone know whats the mean of "m"?
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Old   March 12, 2013, 11:06
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Daniel Duque
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I found this in file src/transportModels/incompressible/viscosityModels/CrossPowerLaw:

Code:
Foam::tmp<Foam::volScalarField>
Foam::viscosityModels::CrossPowerLaw::calcNu() const
{
    return (nu0_ - nuInf_)/(scalar(1) + pow(m_*strainRate(), n_)) + nuInf_;
}
m seems to be some relaxation time in this model. Other than that, I have no idea ...
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Old   March 12, 2013, 11:11
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Dongyue Li
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Quote:
Originally Posted by dduque View Post
I found this in file src/transportModels/incompressible/viscosityModels/CrossPowerLaw:

Code:
Foam::tmp<Foam::volScalarField>
Foam::viscosityModels::CrossPowerLaw::calcNu() const
{
    return (nu0_ - nuInf_)/(scalar(1) + pow(m_*strainRate(), n_)) + nuInf_;
}
m seems to be some relaxation time in this model. Other than that, I have no idea ...
Hi Daniel;



Thanks all the same. in the Cross viscosity equation, it should be like this. and m is the consistency index which dimension is pa*s^n.
Code:
Foam::tmp<Foam::volScalarField>
Foam::viscosityModels::CrossPowerLaw::calcNu() const
{
    return (nu0_ - nuInf_)/(scalar(1) + m_*pow(strainRate(), n_)) + nuInf_;
}
but in Foam, its just like you post the code. So its wired....
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Last edited by sharonyue; March 12, 2013 at 23:02.
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Old   March 12, 2013, 23:16
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Dongyue Li
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Yesterday I just run a case.Actually I dont know what does m mean,But I set it like this:I think its like a kind of gum.

Code:
phase1
{
    transportModel  HerschelBulkley;
rho             rho [ 1 -3 0 0 0 0 0 ] 1000;
HerschelBulkleyCoeffs
{
    nu0             nu0 [ 0 2 -1 0 0 0 0 ] 0.05;
    tau0           tau0 [ 0 2 -2 0 0 0 0 ] 0.01;
    k              k [ 0 2 -1 0 0 0 0 ] 0.2;
    n               n [ 0 0 0 0 0 0 0 ] 0.2;
}
}

phase2
{
    transportModel  Newtonian;
    nu              nu [ 0 2 -1 0 0 0 0 ] 1.48e-05;
    rho             rho [ 1 -3 0 0 0 0 0 ] 1;
   
}

sigma           sigma [ 1 0 -2 0 0 0 0 ] 0.07;

Result of alpha looks okay. in 5 sec, there are some bubbles trapped in the gum.

But nu is not good especially in the final time. When its 5 sec, air is in the top and the gum is in the bottom. but nu is the same all the field.Whats going wrong?

Thanks in advance.
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File Type: jpg h.jpg (97.5 KB, 13 views)
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