coefficient of power-Law viscosity Model in OpenFOAM
 

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

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!!

Hi friends,

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

I have the same problem too...

Cheers,

FS

Dear friends,

I have the same problem as you.

Can someone post an explanation for this problem, plz?

Thank you very much!!

Same problem here. When I divide by density I get very high velocities...

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!

Hi

was anyone able to find the explanation of the units for k in openfoam?
From this thread
http://www.cfd-online.com/Forums/ope...del-blood.html

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