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Old   January 15, 2016, 00:42
Default Question about VOF method
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Zhifang Hu
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I did a two-phase flow simulation using VOF method, with alpha defining as 1 for water and 0 for air.

After the simulation, i tried to do some analysis on water level using sampling along a cross section. The results show there are sampling points with alpha value between 0 and 1, like 0.7 sth.

I am wondering if there is any standard to determine if the point is considered to be air or water based on the alpha value or other factors.

For instance, i may say the point is considered to be water if alpha is bigger than 0.5 at that point, or sth else.

Anyone have any suggestion?

Thanks in advance.
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Old   January 15, 2016, 04:00
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Hi Zhifang Hu,

In VOF method any value between 0 and 1 show the interface.

base on VOF,volume fraction (alpha) is :

volume of liquid that occupy the cell/total volume of cell,therefore,you can

argue that when alpha is 0.7,70% of cell occupied by liquid and 30% occupied

by gas.therefore,in alpha=0.7 you have mixture of gas and liquid that has

more contribution of liquid.
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Old   January 17, 2016, 19:15
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Quote:
Originally Posted by rapierrz View Post
Hi Zhifang Hu,

In VOF method any value between 0 and 1 show the interface.

base on VOF,volume fraction (alpha) is :

volume of liquid that occupy the cell/total volume of cell,therefore,you can

argue that when alpha is 0.7,70% of cell occupied by liquid and 30% occupied

by gas.therefore,in alpha=0.7 you have mixture of gas and liquid that has

more contribution of liquid.
Hi there.

Thanks for the reply.

I do understand the volume fraction alpha, but what i am thinking is that if there is some kinds standard threshold value for alpha to define the point if it can be considered as water or air.

For instance, i can define alpha smaller than 0.5, the point to be air, else is water. or I calculate the point that which the mass of water is more than half to be water cell, or may be alpha is zero for air, else for water. etc

I did some research on it, but nvr find one till now, thats why i am wondering if this kind of threshold exist in defining a point to be water or air.
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Old   January 18, 2016, 03:24
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If you want to do it properly, you will need some sort of geometric reconstruction such as PLIC.
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