# What is phi in simpleFoam

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 October 21, 2008, 23:39 What is phi in simpleFoam #1 New Member   ehsan vaghefi Join Date: Mar 2009 Posts: 9 Rep Power: 8 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 Assistant Moderator   Bernhard Gschaider Join Date: Mar 2009 Posts: 3,915 Rep Power: 40 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 Tushar@cfd and benkematya like this. __________________ Note: I don't use "Friend"-feature on this forum out of principle. Ah. And by the way: I'm not on Facebook either. So don't be offended if I don't accept your invitation/friend request

 September 7, 2011, 11:31 phi Field in Momentum and Eenrgy Equations #3 Member   ,... Join Date: Apr 2011 Posts: 92 Rep Power: 5 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
Join Date: Mar 2009
Location: St. Louis, USA
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Quote:
 Originally Posted by mahdiiowa 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!!
phi is actually a surfaceScalarField, which is different than the vector field. Phi is either interpolated from U (see \$FOAM_SRC/finiteVolume/cfdTools/incompressible/createPhi.H) or is directly calculated in your PISO algorithm and then used in your energy equation if you just added it to icoFoam. so its not exactly the same as your U but is correctly used in your Teqn. Hope that helps.

Dan

 July 22, 2013, 11:10 The units do not seem to match #5 New Member   Sri Join Date: Nov 2012 Posts: 7 Rep Power: 4 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 New Member   eric Join Date: Nov 2010 Location: Vancouver, Canada Posts: 13 Rep Power: 6 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, 11:00 #8 New Member   eric Join Date: Nov 2010 Location: Vancouver, Canada Posts: 13 Rep Power: 6 Thank you very much for the explanation. I am now much clearer with this little guy phi.

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