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about the pEqn in PISO loop of icoFoam

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Old   May 30, 2012, 23:20
Default about the pEqn in PISO loop of icoFoam
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Y. Cao
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I am a beginner of OF, Recently I got some problems when read the code
of icoFoam, in the solver :
fvm::laplacian(rAU, p) == fvc::div(phi)

this is the pEqn defined in the PISO loop of the icoFoam,but, compared to the pressure equation (3.141) described in jasak's thesis(sorry ,I dont known how to inset a formulation here),I think the r.h.s. should be fvc::div(U),because H(U)/aP is assigned to U by "U = rAU*UEqn.H()",
So now I am confused ,could anybody help me ,thanks!
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Old   June 1, 2012, 02:53
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Christian Lucas
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Hi,

fvc::div(U) is correct and it is used in icoFoam. In all incompressible solvers, the equation is divided by density. Therefore, the pressure used in incompressible solvers is actually pressure divided by density.

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Christian
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Old   June 1, 2012, 05:28
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Y. Cao
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Hi, Christian
Thanks for your reply, I known the pressure is divided by density.
but what confused me is that the fvc::div(phi) in the r.h.s. of the p equation given in the source codes of icoFoam.C should be div(U) according to the pressure equation in Jasak's thesis,as far as I known,phi is defiend as the scalar product of velcotiy at the cell surface and the surface vector,obviously,U is not equal to phi.So why they use div(phi)?
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Old   June 1, 2012, 05:42
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Christian Lucas
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Hi, first of all, I have a typo above, fvc::div(U) is wrong and fvc::div(phi) is correct. Sorry about that. Have a look at the eqn 3.141 in jasak's thesis. The second line is exactly what is written in the pEqn of icoFoam. Christian
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Old   June 1, 2012, 22:36
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Y. Cao
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Hi,Chris,thank you very much,
now I get understand,the key problem here is that the fvc::div(phi) isn't to get the divergence of phi, you can not get the divergence of a scalar field, it should be the convection operator, to get the face flux of U, just like div(phi, U) for (UU).
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