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-   -   powerLaw (http://www.cfd-online.com/Forums/openfoam/80586-powerlaw.html)

lgani September 30, 2010 05:26

powerLaw
 
Hi everyone.

Thanks in advance for the help.

I am trying to simulate this power law type fluid behaviour in a pipe flow.

However, I am stuck in the transportproperties file where I have to set the properties of the fluid. I found one thread that says

transportModel powerLaw;

nu nu [0 2 -1 0 0 0 0] 1e-05;

powerLawCoeffs
{
k k [0 2 -1 0 0 0 0] 2500;
n n [0 0 0 0 0 0 0] 0.4;
nuMin nuMin [0 2 -1 0 0 0 0] 0;
nuMax nuMax [0 2 -1 0 0 0 0] 100;
}

I am not sure though how to change my unit of k which is in Pa s^1/n to this unit required by openfoam.
Any idea or help with powerLaw fluid flow ?

Cheers

Locky3827 September 30, 2010 21:04

Hi Leo,
OpenFoam uses a kinematic viscosity so you need to divide the k value by the density of your fluid. You will also need to check your pressure results as the pressure is also divided by the density.
You will also need to check the shear rate used by OpenFoam, if you search the forum there is a thread about that as well (don't know how to put the link in from here).
With laminar pipe flow of a power loaw fluid you can check the results against an analytical result.
Let us know how you get on, there only seems to be a few people doing non-Newtonian flow.
Regards,
Locky

ternik October 1, 2010 02:26

Hi,

your units (normalized with the pressure) for the Power law coefficients are O.K.! It is true that correct unit for the Power law "consistency coefficient" k should be Pa s^(1/n), but I am using the same units and it works!

More important - please note, that the implementation of the shear rate (that is IInd invariant of symmetrical rate of deformation tensor) is not correct (at least in OF-1.5) and it should be:

return sqrt(2.0)*mag(symm(fvc::grad(U_)))

Hope this helps you!

Cheers,
Primoz

Quote:

Originally Posted by lgani (Post 277244)
Hi everyone.

Thanks in advance for the help.

I am trying to simulate this power law type fluid behaviour in a pipe flow.

However, I am stuck in the transportproperties file where I have to set the properties of the fluid. I found one thread that says

transportModel powerLaw;

nu nu [0 2 -1 0 0 0 0] 1e-05;

powerLawCoeffs
{
k k [0 2 -1 0 0 0 0] 2500;
n n [0 0 0 0 0 0 0] 0.4;
nuMin nuMin [0 2 -1 0 0 0 0] 0;
nuMax nuMax [0 2 -1 0 0 0 0] 100;
}

I am not sure though how to change my unit of k which is in Pa s^1/n to this unit required by openfoam.
Any idea or help with powerLaw fluid flow ?

Cheers


Mahyar Javidi August 6, 2012 14:20

Hi
Could anybody tell me when we implement power-law coefficients what is the nu in the line before that? What kind of value I have to implement for it while I am using the power-law coefficients

Regards

nimasam August 6, 2012 14:25

hi mahyar
a newbie question :P
when you choose powerlaw, that mentioned nu is trivial, and the program reads the parameters you defined in powerLawCoeffs

P.S: that nu is for Newtonian transport model

Mahyar Javidi August 6, 2012 16:46

Thanks Nima


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