powerLaw

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 September 30, 2010, 05:26 powerLaw #1 New Member   Leo Pratama Gani Join Date: Sep 2010 Posts: 2 Rep Power: 0 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

 September 30, 2010, 21:04 #2 New Member   Lachlan Graham Join Date: Dec 2009 Posts: 14 Rep Power: 10 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

October 1, 2010, 02:26
#3
Member

Primoz Ternik
Join Date: Apr 2009
Location: Maribor, Slovenia
Posts: 65
Rep Power: 10
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:

Hope this helps you!

Cheers,
Primoz

Quote:
 Originally Posted by lgani 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

 August 6, 2012, 14:20 #4 New Member   anonymous Join Date: Jan 2012 Location: Canada Posts: 24 Rep Power: 8 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

 August 6, 2012, 14:25 #5 Senior Member   Nima Samkhaniani Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,245 Blog Entries: 1 Rep Power: 18 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

 August 6, 2012, 16:46 #6 New Member   anonymous Join Date: Jan 2012 Location: Canada Posts: 24 Rep Power: 8 Thanks Nima

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