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Old   July 30, 2007, 12:25
Default Hi, As I have to make a lit
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As I have to make a little report about the way Foam use to solve the Navier-Stokes, I have some questions to make it clear:

1/ In the SIMPLE algo, why phi is calculated before the correction of U? If phi is calulated after the correction of U, isn't better?

2/i/ I understand that the coefficient aP and aN depend on U. BUT how are they guessed a the FIRST iteration in the SIMPLE algo???? I can not imagine the A matrix actually!
ii/ And the most important: what " /aP" means???
I mean HOW CAN WE DIVIDE by aP which is not a scalar (if I'm not wrong). What does it mean?

3/ To confirm: the previous U is just needed in
the relaxation of UEqn, isn't it?

Any clues or advice, or attempts of answer will be welcome. (and Hrv's reply will be more than appreciated)

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Old   July 30, 2007, 12:41
Default OK, OK. - At the stage wher
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- At the stage where you're looking phi contains only a part of the interpolated velocity dotted with the face area vector. Have a look at phi -= pEqn.flux(); - this is where the rest of the flux comes from and it's after the pressure solution. All is well

- aP is the central coefficient of the momentum matrix, packed up as a field: one value for each cell. That would be a scalar if your discretisation is easy; once you get more clever (than the current implementation), aP will be a 3x3 tensor and division will be a multiplication with the matrix inverse. Advanced, though - for easy stuff have a look at my Thesis

- FIRST SIMPLE iteration: well, you guess U as well, right? That is called the initial guess.

- to confirm: no. You also have it in UEqn.H() - read the forum again, I've explained this.


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