conservative or non conservative, Is there a big difference?

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January 4, 2015, 11:37
conservative or non conservative, Is there a big difference?
#1
Senior Member

Dongyue Li
Join Date: Jun 2012
Location: Torino, Italy
Posts: 743
Rep Power: 9
Hi guys,

Im using twoPhaseEulerFoam to simulate. we can see that in the latest version of OpenFOAM, this two-fluid model is rewritten into conservative form. before this, its non-conservative form.

Right now I know by doing some mathematical rearranging, this two form equations can be the same.

for example, see this formula:

by adding the term in the middle into non conservative form equation, we can get the conservative form equation.

So that means conservative and non-conservative equations can be converted.

But Im confused why sometimes we use non-conservative or conservative form to solve. Besides, we should expect non-conservative and conservative's result should be the same rite?

I quote this from Henry:

Also the fact that 2.3.x is conservative and 2.2.x isn't will affect the results.

can anybody explain this to me? because from formula, there two form's equation are the same one.

Also, I see Alberto is working on this solver to make it conservative, see this:

Quote:
 Originally Posted by alberto [LIST=1][*]Write a two-fluid solver which does not rely on the phase-intensive formulation of the phase momentum equations. The phase intensive form is of great help in stabilizing the solution when the phase volume fraction tends to zero, but it introduces non-conservative terms, which might lead to problems in the solution under certain conditions (See for example Parks et al., Nuclear Engineering and Design, Vol 239, Issue 11, November 2009, Pages 2365-2371)
Generally, conservative form and non conservative form is very different in OpenFOAM?

Waiting for any kind of discussion. Thanks.
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 April 10, 2015, 04:19 #2 Senior Member   Dongyue Li Join Date: Jun 2012 Location: Torino, Italy Posts: 743 Rep Power: 9 I tried to do a comparison with FLUENT, Im sure 22x's result is better(non-conservative equations) This happens on stirred tank using MRF.

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