# Volume fraction constant

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 January 31, 2006, 18:04 Volume fraction constant #1 Shanti Guest   Posts: n/a Hi Could someone tell me how to keep the volume fraction of a particular phase constant in the VOF method? Thanks in advance... shanti

 February 1, 2006, 02:18 Re: Volume fraction constant #2 Ynot Guest   Posts: n/a what do you mean?

 February 1, 2006, 04:00 Re: Volume fraction constant #3 kharicha Guest   Posts: n/a 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 ?

 February 1, 2006, 11:54 Re: Volume fraction constant #4 Shanti Guest   Posts: n/a 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?

 February 1, 2006, 15:30 Re: Volume fraction constant #6 Shanti Guest   Posts: n/a 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.

 February 1, 2006, 15:39 Re: Volume fraction constant #7 Ynot Guest   Posts: n/a 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?

 February 1, 2006, 15:41 Re: Volume fraction constant #8 Shanti Guest   Posts: n/a yes. I am using VOF only.i have defined the boundary condition at the top surface as volume fraction of phase-2 is zero.

 February 1, 2006, 15:44 Re: Volume fraction constant #9 Ynot Guest   Posts: n/a 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.

 February 5, 2006, 00:23 Re: Volume fraction constant #10 Ynot Guest   Posts: n/a 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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