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Old   January 13, 2004, 14:09
Default two-phase flow
  #1
subhu
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i am simulating air-water flow in a straight pipe(2-D & 3-D) usinf VOF model.It is stratified flow regime.Water is the primary phase. In VOF we give the mixture velocity which is the average of both the velocities. But then how do we get the velocity of individual phases after simulation.
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Old   January 14, 2004, 04:43
Default Re: two-phase flow
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mateus
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Hi!

I'm not shure if you can do that...The vof model concerns the mixture of 2 phases as one individual phase. You should work with eulerian model, where you solve ns equations for each phase, to do this. Maybe mixture model wit "slip velocity" can also be used...

regards

MATEUS
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Old   January 14, 2004, 09:04
Default Re: two-phase flow
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ozgur
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Hi,

Fluent says that VOF should be used for stratified & free surface flows. But, as you've said, VOF solves it like a single phase with changing properties. I am also not clear about this. I try to simulate single falling droplet with VOF. I would expect independent velocity fields in and out of the drop, but the fields I obtained with VOF are not so (they seem to be continuous). I also tried Eulerian, but results again are not satisfying. I have a doubt that drop interphase boundary conditions are taken into account with those models. (Eulerian model does not even require surface tension which has obviously an influence on the solution!!)
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Old   January 14, 2004, 09:06
Default Re: two-phase flow
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ozgur
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Hi,

I think you can patch the velocities independently for each of the phases.

Regards
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Old   January 14, 2004, 17:26
Default Re: two-phase flow
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hadi
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Hi, you can get the individual velocity by assigning the volume fraction of phases in BC. select phase 2 (secondary phase no mixture) and set the 1 or 0 for volume of fraction. Note for assigning phases that better choice for water phase is phase2 because patch of secondary phase is easier than primary phase
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Old   January 31, 2004, 01:35
Default Re: two-phase flow
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prasanth
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hi ppl, repeating same old question, In your view, which is the better model and some suggestions for simulating a closed vertical cyl. tank with liq. hydrogen filled upto some 80% and remaining filled with vapor hydrogen, a constant heat flux is applied on side walls (cyl. wall) or all sides. We have to simulate natural convection and thermal stratification in it and surface evaporation at liq. vap interface at saturation.
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