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VOF Modelling

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Old   July 31, 2015, 08:40
Unhappy VOF Modelling
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Thiago
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Hello!!

I am a new Fluent user. I started working on my Master Thesis right now and it involves Fluent/CFD;

I need to model a single elongated bubble (Taylor bubble) flowing within a column of stagnant liquid.

I know I should use VOF model for that since I want to track the bubble advance within the liquid pipe.

Someone can help me with that? How can I start implementing this problem, like boundary and initial conditions and how to introduce a single bubble in this problem? I read Fluent Tutorial and user s guide but it did not help me very much....

Thanks since then
I really appreciate if you can help me with that....
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Old   August 17, 2015, 08:17
Default VOF Modelling
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Hi
in summary you have to do the following steps:
1- create your model
2- generate a good mesh (structured mesh is better)
3- setup your physical model like as unsteady, two phase, turbulence, ...
4- choose VOF model (obviously you have not mass or heat transfer)
5- choose liquid as a primary phase and air or gas as a secondary phase
6- active gravity and define gravity in the correct direction
7- initialize the problem in which the you domain will be filled by primary phase
8-** you have to patch the secondary phase (initial place of bubble)
: you have to mark an adapted region (bubble initial place) in adaption form
9- run
as you know these steps are the most important. if you want some more detail, I can help you.
by the way see these link:
http://www.aparat.com/v/QSApg
http://www.aparat.com/v/3mMhf
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Old   August 17, 2015, 08:40
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Thanks a lot, mrkelich!!!

I really aprecciate it!

Actually, I made it and my main worry right now is to plot a transient chart: velocity of the bubble front versus time. Do you have any idea on how doing that without coding???
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Old   August 17, 2015, 08:46
Default velocity
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I have not fluent software in front of mine right now. I'll tell you as soon as possible.
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Old   August 17, 2015, 08:51
Default velocity
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the simplest but the poorest way is you create a pint almost in center of bubble at some times, read the velocity and then plot it manually. as you know the velocity is almost equal entire of bubble
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Old   August 18, 2015, 09:11
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mrkelich, how can I read the velocity at any point inside the bubble? There is any function in Fluent which can do that for me?
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Old   August 18, 2015, 09:29
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actually i need to track the bubble nose velocity, do you know how can i do that?
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Old   August 18, 2015, 15:39
Default bubble
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1- Go to surface (in main menu bar) and choose the Point
2- You can use the select point with mouse for visual selecting or enter the any point coordinate
Draw contour (phases : phase-2 manual range 0.9-1) to capture bubble boundary and select the point by Right Mouse Click)
3- create the pint
4- finally you can read the flow parameters by plot or reports options.
as I told this is the simplest and poorest way.
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Old   August 20, 2015, 12:56
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Many thanks, man!

I have one final question and I wonder if you could help me out with this one:

I am trying to set up a Taylor bubble 2D flowing within a column of stagnant liquid.

Initially I have water on the top of the tube and gas below it. They are initially separated from each other.

What I need to do is the following: It is necessary to disturb the interface in the 2D axisymmetric simulations in order to have a flow. The
interface can be disturbed by setting the gravity in the opposite direction for a small time of period. After the interface was disturbed the gravity was set in the normal downward orientation again. Immediately thereafter a bubble was seen to move upward as the liquid was falling downward.

How can I do that??? Disturbing the interface?

Thank you man
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Old   August 22, 2015, 01:10
Default taylor
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you have to patch your domain, liquid is on the top of the tube and gas below it at t=0., and also setup gravity in the right direction.
personally I prefer to do in 3d than ax-symmetric.
send your email and I'll send you an example of Taylor bubble in 2d.
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Old   August 22, 2015, 06:32
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Yes, I did what you said. Actually I need to model it first in 2D case... I guess the problem is on which direction should I set the interface in order to dirturb it in the beginning. I know that after the interface is disturbed I set the gravity in the -y direction. But in the beginning is problem....

Anyway, my email is tsaumagomes@poli.ufrj.br

I really appreciate your help!!!
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Old   September 5, 2015, 02:32
Smile 2d bubble column simulation
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hello sir
i would like to know how to model if we have separate inlet for gas and liquid (liquid column is not stagnant)which is flowing in same direction.
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