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Old   May 11, 2006, 04:34
Default Gas/Liquid with VOF
  #1
rt
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In the multiphase option of fluent with VOF method it is possible to define primary phase (e.g. gas) as ideal gas and secondary phase (tracked phase e.g. liquid) as incompressible,

What is the fluent's model for this? what is method of cupling between this two model (incompressible and probably compressible) it is especially confusing for interfaces cell. If anyone have information about this or knowe the refrence of it, please give me guide.

with Regard.

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Old   May 11, 2006, 10:09
Default Re: Gas/Liquid with VOF
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Renato.
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Hi RT,

why are you willing to consider the gas phase as an ideal gas?

I'm not a Fluent user, so I don't know regarding the Fluent's VOF formulation, but I could say that when working with interface between gases and liquids it's common to treat gas+liquid as it was only one incompressible fluid with properties varying. It's perfect understandable since most of the inertia is due the liquid phase. In this sense you can solve your liquid phase and forget about the gas phase. Furthermore, some modern solvers don't solve the gas phase. In this case the solver runs faster since it does not lose time solving the fluid flow in some region where we're not interested.

Regards

Renato.
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Old   May 11, 2006, 10:41
Default Re: Gas/Liquid with VOF
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rt
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Your discussion is correct and is well-known, but i am confused that how fluent treat incompressible and ideal gas simulteneously!, there is not any material about this in fluent help.

But about why ideal gas assumption !!! as i model mold filling problem, incompressible assumption of gas needs design of some outflow for gas exhasing that is not simple task for complex geometry also this increase ill-poseness of system and increase computational cost.
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Old   May 11, 2006, 11:42
Default Re: Gas/Liquid with VOF
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Renato.
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I see what you mean...

Couldn't you consider that the gas phase can exit the mold without constraints? By this way you could neglect the compressibility effects... Is your mold completely closed?

I'm sorry because I can't help you with Fluent, but I would suggest a nice paper related to mold filling that I read recently:

Hetu, JF and Ilinca Florin, "A Finite Element Method for Casting Simulations", Numerical Heat Transfer, Part A, 36:657-679, 1999

in this paper some assumptions regarding your problems are discussed.

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Old   May 11, 2006, 11:58
Default Re: Gas/Liquid with VOF
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rt
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The effect of gas don't have importance for me because my mold is porous (silica sand mold) and gas easily goes out from it.

Also please send to me the mentioned paper:rohtav@yahoo.com

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