Equation discretisation in icoFoam

kar · February 9, 2008, 14:18

Hello,

looking at the icoFoam solver code, I don't understand how U*(div(U)) is represented by fvm::div(phi,U). Could you please explain?

k.

mike_jaworski · February 10, 2008, 00:48

Hello Karlis,

If you take a look in the Programmers guide, page P-38 discusses the way OpenFOAM discretises the convection term. In addition, Table 2-2 a couple pages above that tells you that when you write out the convective derivative this way: div(phi, U), that the first field (phi) has to be a surface scalar field. So, during the initiation of the PISO loops, I believe, this phi surface scalar field is created which represents the divergence of the velocity field.

I hope that helps.

Regards,
Mike J.

P.S. The programmers guide can be downloaded from the "documentation" section of the OpenCFD website.

kar · February 10, 2008, 05:12

Hello,

My question was wrong - div(Ui*U), i = 1,2,3 is represented by fvm::div(phi,U). I would think, flux phi is used later to avoid volume integration, so I still don't understand this one..

Looking at ProgrammersGuide p. 38, equation 2.16 - why is Sf&(ro*U)_f just rewrited as "F"? I think is should be interpolated and integrated somehow.

Also from which time step U values are taken? I guess old one, else, how fvMatrix could be solved..

hjasak · February 10, 2008, 06:34

Why don't you just take a look at my Thesis - it goes through it step by step.

Hrv

February 9, 2008, 14:18	Hello, looking at the icoFo	#1
kar Senior Member Kārlis Repsons Join Date: Mar 2009 Location: Latvia Posts: 111 Rep Power: 17	Hello, looking at the icoFoam solver code, I don't understand how U*(div(U)) is represented by fvm::div(phi,U). Could you please explain? k.

February 10, 2008, 00:48	Hello Karlis, If you ta	#2
mike_jaworski Senior Member Michael Jaworski Join Date: Mar 2009 Location: Champaign, IL, USA Posts: 126 Rep Power: 17	Hello Karlis, If you take a look in the Programmers guide, page P-38 discusses the way OpenFOAM discretises the convection term. In addition, Table 2-2 a couple pages above that tells you that when you write out the convective derivative this way: div(phi, U), that the first field (phi) has to be a surface scalar field. So, during the initiation of the PISO loops, I believe, this phi surface scalar field is created which represents the divergence of the velocity field. I hope that helps. Regards, Mike J. P.S. The programmers guide can be downloaded from the "documentation" section of the OpenCFD website.

February 10, 2008, 05:12	Hello, My question was wron	#3
kar Senior Member Kārlis Repsons Join Date: Mar 2009 Location: Latvia Posts: 111 Rep Power: 17	Hello, My question was wrong - div(UiU), i = 1,2,3 is represented by fvm::div(phi,U). I would think, flux phi is used later to avoid volume integration, so I still don't understand this one.. Looking at ProgrammersGuide p. 38, equation 2.16 - why is Sf&(roU)_f just rewrited as "F"? I think is should be interpolated and integrated somehow. Also from which time step U values are taken? I guess old one, else, how fvMatrix could be solved..

February 10, 2008, 06:34	Why don't you just take a look	#4
hjasak Senior Member Hrvoje Jasak Join Date: Mar 2009 Location: London, England Posts: 1,905 Rep Power: 33	Why don't you just take a look at my Thesis - it goes through it step by step. Hrv __________________ Hrvoje Jasak Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk

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