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-   -   nonNewtonianIcoFoam, wired nu (http://www.cfd-online.com/Forums/openfoam-solving/114413-nonnewtonianicofoam-wired-nu.html)

sharonyue March 10, 2013 23:19

nonNewtonianIcoFoam, wired nu
 
2 Attachment(s)
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.

sharonyue March 12, 2013 09:06

Does anyone know whats the mean of "m"?

dduque March 12, 2013 11:06

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 ...

sharonyue March 12, 2013 11:11

1 Attachment(s)
Quote:

Originally Posted by dduque (Post 413463)
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....

sharonyue March 12, 2013 23:16

2 Attachment(s)
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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