Zero Volume Fraction in Free Surface Problem

marega · September 10, 2009, 04:11

Hi all,
i got a question about the calculated Volume Fraction in CFX 12.0.
I am trying to simulate a free surface problem pretty similar to the flow over a bump tutorial, where there is a distinct free surface between Air and a liquid.
It works pretty well, but there is still liquid volume fraction in the air of about 10^-15. My question is, since i am pretty new in CFD, is it generally possible to get a liquid volume fraction of zero in the air region (or similar: air volume fraction in the liquid region) or is it not possible?

I wasnt able to finde an answer for that in the documentation nor in this forum.

regards

ghorrocks · September 10, 2009, 07:31

1e-15 is the minimum value for volume fraction. It is not allowed to go below this as otherwise you can get boundedness problems - that is volume fractions smaller than zero or greater than one.

September 10, 2009, 04:11	Zero Volume Fraction in Free Surface Problem	#1
marega New Member Join Date: Aug 2009 Posts: 1 Rep Power: 0	Hi all, i got a question about the calculated Volume Fraction in CFX 12.0. I am trying to simulate a free surface problem pretty similar to the flow over a bump tutorial, where there is a distinct free surface between Air and a liquid. It works pretty well, but there is still liquid volume fraction in the air of about 10^-15. My question is, since i am pretty new in CFD, is it generally possible to get a liquid volume fraction of zero in the air region (or similar: air volume fraction in the liquid region) or is it not possible? I wasnt able to finde an answer for that in the documentation nor in this forum. regards

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September 10, 2009, 07:31		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	1e-15 is the minimum value for volume fraction. It is not allowed to go below this as otherwise you can get boundedness problems - that is volume fractions smaller than zero or greater than one.