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When to set momentumPredictor to Yes

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Old   March 14, 2006, 23:58
Default Hi, Can someone tell me und
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Pei-Ying Hsieh
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Hi,

Can someone tell me under what condiction should momentumPredictor be set to yes? Thanks!

Pei
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Old   March 15, 2006, 06:35
Default As far as I understand, in the
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Pierre Le Fur
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As far as I understand, in the pressure-velocity algorithm for two-phase flows in Foam does not need the momentum equation to be solved, so in general momentumPredictor should be set to no, especially for "challenging" test cases (i.e if there is problems with convergence or sharp volume fractio gradient). In this case the momentum equation is only constructed and used to obtain fluxes and solve the pressure equation. On the other hand solving the momentum eqaution might speed up convergence in non-challenging steady-state calculations.

Hope that helps

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Old   March 15, 2006, 15:54
Default Thanks Pierre! How about tu
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Pei-Ying Hsieh
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Thanks Pierre!

How about turbFoam?

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Old   March 16, 2006, 15:07
Default TurbFoam uses the standard PIS
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Pierre Le Fur
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TurbFoam uses the standard PISO algorithm, momentum equation is always solved. it can be used for unsteady or steady cases.

Pierre,
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Old   January 22, 2009, 06:53
Default Hi together, for me it is n
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Marc Wattenberg
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Hi together,

for me it is not clear where the velocity field is coming from when the momentum equation is not solved. perhaps it is a stupid question but for the moment a need a hint

thanks
marc
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Old   January 22, 2009, 07:32
Default U = U* - grad(p)/A where U*
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Eugene de Villiers
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U = U* - grad(p)/A

where U* = H/A

i.e. U is solved explicitly after the pressure equation.
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Old   January 22, 2009, 12:25
Default Hi Marc, It depends on the
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Hrvoje Jasak
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Hi Marc,

It depends on the importance of the laplacian in the momentum equation: if you have important diffusivity in the momentum, you should solve the momentum equation implicitly.

Enjoy,

Hrv
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Old   March 16, 2010, 05:16
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Claus Meister
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Hey Foamers,

I read your posts. Could anybody tell me where to find a direct statement about this, i.e. no long text. Friends referred me to Ferziger. But I cannot find the right page.

Cheers
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Old   March 16, 2010, 08:27
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Sandy Lee
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I want to know too. I guess, if we set no, maybe it is slow to get convergence to some cases, but they will get the same results, right? Who can give some light?
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Old   March 17, 2010, 03:10
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matej forman
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Dear Claus,

Ferzinger , Peric, Comput. Methods for Fluid Dynamics is very good book and I guess you should read it all anyway. But not to waste your time, have a look at chapter 7.5 as a start. Also these slides from stanford I googled my appeal:http://www.stanford.edu/class/me469b...mpressible.pdf

As a good quote from this site sais: "Two weeks of playing with a CFD code will save you one afternoon of reading". (sorry, I forgot the author).

good luck
matej
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