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Volume fraction constant

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Old   January 31, 2006, 18:04
Default Volume fraction constant
  #1
Shanti
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Hi

Could someone tell me how to keep the volume fraction of a particular phase constant in the VOF method?

Thanks in advance...

shanti
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Old   February 1, 2006, 02:18
Default Re: Volume fraction constant
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Ynot
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what do you mean?
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Old   February 1, 2006, 04:00
Default Re: Volume fraction constant
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kharicha
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so you have minimum three phases....two are position and time dependent and one is fixed...

question do you also fix the velocity of the fixed phase ?
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Old   February 1, 2006, 11:54
Default Re: Volume fraction constant
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Shanti
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I am modelling a mould which is partially covered with one fluid.So i have 2 phases..polymer fluid and air. I want to give an intial disturbance to it and study the interface of the fluid. For this I want to keep the volume fraction of the polymer fluid constant. How can i do it?
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Old   February 1, 2006, 15:27
Default Re: Volume fraction constant
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Ynot
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From i understood, you want to initialize part of your domain with a volume fraction of 1 for the polymer, while the rest is air.

If this is so, you need to patch the desired part of your domain.

The simplest way to do it is as follows Adapt/Region Here, you create the region that you want to be initialized with polymer. The easiest is to create a quadrilateral (if the problem is 2d). Choose your quad limits and click "Mark". This will marck the cells that belong to that quad.

Once done, go and initialize your solution. Initialze all your domain to be filled with air.

Now go to Solve/initialize/patch

and patch the quad you have created with your desired fluid.

Tell me if this is what you had in mind.

Best,

Ynot - Tsaad
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Old   February 1, 2006, 15:30
Default Re: Volume fraction constant
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Shanti
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yes..you described my model exactly. When i am iterating, the contours are showing that the entire domain is covered with phase-2 (polymer fluid)..so can we define its volume fraction to be constant.
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Old   February 1, 2006, 15:39
Default Re: Volume fraction constant
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Ynot
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well, the polymer fluid has a much larger density than the air so except in "out of this world" situations, the polymer should not fill out your domain at all, right?

are you using VOF? If you are, then i suggest you use the implicit euler.

another problem is with the discretization schemes. Some schemes are diffusive when used with the VOF, and as soon as you iterate, you get irrealistic mass fractions.

The time step is also extremely important. Your phenomenon has very small time scales, so you have to use a very small time step.

What boundary condition are you using for the simulating the air disturbance?

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Old   February 1, 2006, 15:41
Default Re: Volume fraction constant
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Shanti
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yes. I am using VOF only.i have defined the boundary condition at the top surface as volume fraction of phase-2 is zero.
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Old   February 1, 2006, 15:44
Default Re: Volume fraction constant
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Ynot
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Ok, what are your Dynamic BCs?

at the top surface, is it a pressure inlet, a velocity inlet?

if you could describe the geometry a bit, it would be easier.

is it a rectangular container and your polymer is at the bottom? then i suggest that you initiate your disturbances from the left.
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Old   February 5, 2006, 00:23
Default Re: Volume fraction constant
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Ynot
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Did you solve it? I think i know how to get it running. Tell me if you found a way around it.

Ynot - Tsaad
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