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adma February 1, 2006 13:14

CFX bubble simulation with free surface model
 
hi

I am trying to simulate a single big air bubble (say 1cm in diameter) rising from the bottom of a water tank trasiently.

I set up initial VOF in the way that air (VOF=1) will occupy a spherical space 7cm under the water level. I also choose free surface options in simulation. I set water as primary fluid with surface tension as 0.072N/m.

The simulation can run and the bubble does rise. It even looks like breaking into two bubbles (is that correct?). But what confuses me is, except for the initial condition, there is no clear boundary between air and water anymore. For instance, air VOF is 0.5 while water VOF is 0.5 somewhere in spite that place with higher air VOF look like a bubble shape.

what did I do wrong?

BTW: can anyboday recommend several papers about similar research or books about air bubble in water stability?

Thank you very much for your reading!


adma February 1, 2006 13:15

Re: CFX bubble simulation with free surface model
 
forget. I am using CFX5.7

Camilo Costa February 2, 2006 08:22

Re: CFX bubble simulation with free surface model
 
I think that your initial condition was wrong. You need set one interface clear between water and air. Whow you set your initial vof for water and air?

adma February 2, 2006 10:55

Re: CFX bubble simulation with free surface model
 
thank you for your reply. I did set initial condition. I checked the initial condition file (0_full.trn). It clearly shows there is clearly boundary (a bubble) between air and water where volume fraction of air=1 and VF water=0 forming a bubble shape. I also set gravity direction and buoyancy density. The bubble rises, but the boundary just blurred more and more. It doesn't make sense.

did you used to do similar simulation with cfx5? Is that possible I can look at an sample cfx5 definition file? I need help urgently. My email is stonebrook2005@yahoo.com

Regards

Camilo Costa February 3, 2006 07:28

Re: CFX bubble simulation with free surface model
 
Can existed many factors that influence in your problem! The solution is not god, The modelation is not god or the mesh is not appropriate!! Can i help you if i donīt know the origen of problem!

You use adaptive mesh in your problem?

Send me your *.gtm and *.cfx file for i look and indentife the problem for you!!

forgive my bad english!!

adma February 3, 2006 09:50

Re: CFX bubble simulation with free surface model
 
I used a pretty coase meth casue i wanted to make it run alright first before changing to finer mesh. would you leave me an email? I will send you the files.

thanks a lot!

Camilo Costa February 3, 2006 12:17

Re: CFX bubble simulation with free surface model
 
costa_augusto@labsolar.ufsc.br

I make one simulation of your problem and the results are good!! I donīt set the superficial tension!! Ineed study more this!!


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