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coefficient of power-Law viscosity Model in OpenFOAM

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Old   February 23, 2014, 13:16
Default coefficient of power-Law viscosity Model in OpenFOAM
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Daniel
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Hello foamers

I have searched a lot but I was not able to find any proper explanation about coefficient of power-Law viscosity Model.

I have used online curve fitting tools to determine constant coefficients in power-Law viscosity model based on my experimental data. These values are obtained for k and n:

k = 0.0102 [Pa.s^(n)]

n = 0.46

Now when it comes to OpenFOAM, it uses kinematic viscosity and after reading source code of power-Law viscosity model, I have found out that k has the same dimension as nu.

I have divided my k value by rho and that gives me:

k = 7.293e-6

However, when I use this value for k the solution diverges quickly. I have seen a few tutorials in which k has a very large magnitude like 2500.

Am I missing something here? maybe I did not understand the model properly.

best wishes

regards
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Old   March 23, 2014, 17:30
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Nadish Saini
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Hello Daniel,
Were you able to find a good explanantion for the power law model. I am also a little confused as to why k value is taken so large in some cases. If i take k value small, the solution is not converging. Please help!!
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Old   July 7, 2014, 00:46
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Filippo
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Hi friends,

Have you found a solution for this problem that you can share with me?

I have the same problem too...

Cheers,

FS
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Old   September 21, 2014, 03:06
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Alexa
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Dear friends,

I have the same problem as you.

Can someone post an explanation for this problem, plz?

Thank you very much!!
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Old   January 28, 2015, 09:05
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Jonas
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Same problem here. When I divide by density I get very high velocities...
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Old   January 28, 2015, 15:29
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Nadish Saini
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Hi,
I had this problem some time back. Someone suggested to initiate the flow with constant viscosity. The k value is supposed to be large (if i remember correctly). So yeah, i ran a few time steps with constant viscosity and then switched to power law model and that allowed the simulation to run smoothly. Try that!
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Old   April 5, 2016, 04:23
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Ananthakrishnan.A.S
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Hi

was anyone able to find the explanation of the units for k in openfoam?
From this thread
Power-law viscosity model for blood

i understand that openfoam multiples strain rate by one sec, so k does not have n in its power but how to eliminate sec from SI units. I get the values of k experimentally in pa.s^n. I dont know how to incorporate this into openfoam

Thanks
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