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October 21, 2008, 23:39 
What is phi in simpleFoam

#1 
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ehsan vaghefi
Join Date: Mar 2009
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Hi there
I have been using simpleFoam to solve my problem, I was wondering the what is the "phi" file that openFoam is calculating ? a more general question , can calculate fluxes (as vectors) on each of nodes ? Cheers. Ehsan 

October 22, 2008, 07:14 
As this phi question creeps up

#2 
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Bernhard Gschaider
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As this phi question creeps up every 2 weeks or so, I thought it might be a good candidate for the FAQ: http://openfoamwiki.net/index.php/Main_FAQ#What_is_the_field_phi_that_the_solver _is_writing
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September 7, 2011, 11:31 
phi Field in Momentum and Eenrgy Equations

#3 
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,...
Join Date: Apr 2011
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Hi Everybody
I have added temperature equation to icoFoam in the manner that has been described in http://openfoamwiki.net/index.php/Ho...ure_to_icoFoam The main part is fvScalarMatrix TEqn ( fvm::ddt(T) + fvm::div(phi, T)  fvm::laplacian(DT, T) );From a mathematical manipulation i founded out that phi should be "ui + vj" here. And this vector form for phi is in complete disagreement with what has been described for the field phi in the following page  "http://openfoamwiki.net/index.php/Main_FAQ" in section "3.1.3 What is the field phi that the solver is writing" "3.1.3 What is the field phi that the solver is writing " The answer in this file is the mass flow through the cell faces ( with the area of the face).  In Summary: Do you guys know whether phi is different in the vector form of the momentum equation and scalar temperature equation! What I had founded out is that YES, it should be different. But I am NOT sure! I would appreciate if someone helps me!! 

September 7, 2011, 18:25 

#4  
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Daniel P. Combest
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Location: St. Louis, USA
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Quote:
Dan 

July 22, 2013, 11:10 
The units do not seem to match

#5 
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Sri
Join Date: Nov 2012
Posts: 10
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Hi,
Is Phi just U dotted on to A or rhoU dotted on to A as you have described on the page. The table has units cu.m/s which would fit the first description of Phi (U dotted on to A). Thanks, Sri 

September 28, 2013, 02:21 

#6 
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eric
Join Date: Nov 2010
Location: Vancouver, Canada
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I just start learning FOAM and also have the same question about phi.
In the equation of motion UEqn, phi seems to be rho*U. But in the equation of energy TEqn, phi is U. This phi bothers me a lot. Can anyone explain it please. Thanks in advance. 

September 29, 2013, 06:37 

#7 
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Bruno Santos
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Greetings to all!
openfoamwiki.net is undergoing some changes on the FAQ section. I've updated the FAQ associated to this thread's topic: http://openfoamwiki.net/index.php/FA..._is_writing.3F @Eric: You didn't mention which solver you were looking at, but the answer should be simple: compressible solvers use the rho field; incompressible solvers do not use the rho field. If look at the user guide, section "2.1.1.3 Physical properties", you'll see that the fluid density is implied when using "kinematic viscosity nu": http://www.openfoam.org/docs/user/cavity.php Best regards, Bruno PS: I also merged the two threads where Eric had posted, because it made sense to keep the two threads in a single discussion.
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September 29, 2013, 11:00 

#8 
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eric
Join Date: Nov 2010
Location: Vancouver, Canada
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Thank you very much for the explanation. I am now much clearer with this little guy phi.


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