Question; Where does one draw the line between water and air?

Alwinder Singh · July 2, 2018, 04:21

Hello fellow Foamers

I'm new to the Field of CFD and writting my Bachelor Thesis about a mesh analysis in OpenFoam (VOF;InterDyMFoam).
(yes i learned it is a long way, notheless a fun one

)

So in a meeting with my supervisior we stumbeld over a simple (or not) question.

Where is the phaseline between water and air in a VOF simulation?

So while in the real world the phase transition of water and air is quite visible, in a VOF simulation it isn't.

Mostly because the Voluminas which contain the data are calculated with a ratio of Air and Water in it.

What kind of ratio would you use for the phase transition?

Well now i've written 2 questions which are kinda related maybe even the same.

Feel free to comment/discuss.

My answers for the questsions would be:

In a real world we see the watersurface so this line constist of 100% (ok 95%) water. Which then results in a ratio of 0.95 to 0.05 (water:air).

Thanks for your comments and inputs!

Happy Day to you.

Alwinder

(First Post YAY

)

arjun · July 2, 2018, 04:54

There is no distinct line here and sometimes there is no line at all.

The separation is all very subjective and depend on the users. Most of the time the line of separation is assumed to be where volume fraction is equal to 0.5 but you could chose other values and call it the line that is dividing two phases.

July 2, 2018, 04:21	Question; Where does one draw the line between water and air?	#1
Alwinder Singh New Member Alwinder Singh Join Date: Jun 2018 Posts: 1 Rep Power: 0	Hello fellow Foamers I'm new to the Field of CFD and writting my Bachelor Thesis about a mesh analysis in OpenFoam (VOF;InterDyMFoam). (yes i learned it is a long way, notheless a fun one ) So in a meeting with my supervisior we stumbeld over a simple (or not) question. Where is the phaseline between water and air in a VOF simulation? So while in the real world the phase transition of water and air is quite visible, in a VOF simulation it isn't. Mostly because the Voluminas which contain the data are calculated with a ratio of Air and Water in it. What kind of ratio would you use for the phase transition? Well now i've written 2 questions which are kinda related maybe even the same. Feel free to comment/discuss. My answers for the questsions would be: In a real world we see the watersurface so this line constist of 100% (ok 95%) water. Which then results in a ratio of 0.95 to 0.05 (water:air). Thanks for your comments and inputs! Happy Day to you. Alwinder (First Post YAY )

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July 2, 2018, 04:54		#2
arjun Senior Member Arjun Join Date: Mar 2009 Location: Nurenberg, Germany Posts: 1,273 Rep Power: 34	There is no distinct line here and sometimes there is no line at all. The separation is all very subjective and depend on the users. Most of the time the line of separation is assumed to be where volume fraction is equal to 0.5 but you could chose other values and call it the line that is dividing two phases.