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-   -   CVMcoefficient in bubblefoam (http://www.cfd-online.com/Forums/openfoam-solving/59892-cvmcoefficient-bubblefoam.html)

 stephan December 17, 2006 06:45

hi all, i was wondering if

hi all,

i was wondering if the coefficent cvm in bubblefoam can be set to zero or does this term essentially takes care of conserving the momentum by correcting the momentumequation with the help of the relative velocity?
any help is welcome
stephan

 msrinath80 December 17, 2006 13:15

I have no experience with bubb

I have no experience with bubblefoam yet. However the name "cvm" rings a bell. Maybe it is one of the interfacial forces? Coefficient of Virtual Mass perhaps? To my knowledge this is significant only when the dispersed phase (bubbles/drops) accelerate/decelerate. If this is set to zero, then you're assuming that the bubble/drop flow is primarily steady in the sense that there is no acceleration/deceleration when it moves subject to the fluid forces on it. "cvm" may also be present (albeit deeply embedded) in the k-e turbulence model.

I could of course be completely wrong about "cvm" referring to the coefficient of virtual mass. So you might want to wait for someone else to chime in.

 stephan December 18, 2006 07:21

hi, thanks a lot for your i

hi,

thanks a lot for your ideas! i will take a look at the turbulence-equation and figure out if that term is causes by turbulence.
any other ideas?
stephan

 stephan December 18, 2006 09:42

hi, the term in cvm seems t

hi,

the term in cvm seems to be a kind of added or virtual mass concept.
if one adds the cvm-terms of both momentumequation (after mulplying each phase-term with its density and its volumefraction) it will become zero.
so the effect vanishes for the the overall momentumequation as it should be.
stephan
p.s. but maybe one of the developers will give a short "yes" or "no"?!

 hemph December 19, 2006 02:48

If a particle or bubble is to

If a particle or bubble is to be accelerated in a fluid field, one needs to take into account that also the surrounding fluid needs to be accelerated. This can be seen as the particle having added, or "virtual" mass. For a single particle, the coefficient is usually 0.5, but if you do not wish to simulate this effect, it can be set to zero. As pUl|said in the above posting, it is only important if there is a acceleration in your flow case.

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