# free surface in Fluent ?

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 November 16, 2000, 08:02 free surface in Fluent ? #1 Mounir Guest   Posts: n/a I am simulating a stirred tank. First for one phase and in the next step for 2 phases (gas dispersion in water using the Algebraic Slip Mixture Model (ASMM). I want to define the top surface of the liquid as free surface. how shoud the top surface of the tank be defined in Gambit (outflow? wall? outlet pressure??) many thanks Mounir

 November 17, 2000, 03:03 Re: free surface in Fluent ? #2 Harry Guest   Posts: n/a define it as wall, but set in FLUENT as specified stress, set 0 for all variable

 November 17, 2000, 11:56 Re: free surface in Fluent ? #3 Peter Staykov Guest   Posts: n/a Hi Mounir, I am solving a problem similar like your's. If you want to simulate the top surface of the liquid as a free surface you must use two-phase model. The first phase is the liquid in the tank and the second phase is the air above the liquid surface. So, you need to modify your grid file so that the air to be included above the reactor. After this you can read your modified grid file into Flient and can use some of multiphase model - VOF by example. It is convenient to define the air as a primary phase and the water as a secondary one. After the initialiazation of the solution you must patch the water-liquid fraction value 1 and start the iterations process. Keep in mind that the multuphase calculations are very CPU intensive. If you have any other questions, please do not hesitate to ask me. I hope I can answer to you.

 November 17, 2000, 14:02 Re: free surface in Fluent ? #4 Sandeep Guest   Posts: n/a Please go and check the example problem in the fluent tutorial guide : vol 3. Its about water and air in a spinning bowl. It should provide as a good start to set up your VOF problem.

 November 21, 2000, 12:00 Re: free surface in Fluent ? #5 Narayanan Guest   Posts: n/a you have to define it has symmetry boundary condition. if you are using algebraic slip model u cannot have transient conditions and also u cannot have mixture of particles or discrete phase. i would like you to check the same.

December 23, 2011, 17:22
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Pooya
Join Date: May 2010
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Quote:
 Originally Posted by Peter Staykov ;95458 Hi Mounir, I am solving a problem similar like your's. If you want to simulate the top surface of the liquid as a free surface you must use two-phase model. The first phase is the liquid in the tank and the second phase is the air above the liquid surface. So, you need to modify your grid file so that the air to be included above the reactor. After this you can read your modified grid file into Flient and can use some of multiphase model - VOF by example. It is convenient to define the air as a primary phase and the water as a secondary one. After the initialiazation of the solution you must patch the water-liquid fraction value 1 and start the iterations process. Keep in mind that the multuphase calculations are very CPU intensive. If you have any other questions, please do not hesitate to ask me. I hope I can answer to you.
Hi Peter
in the same problem but in the open channel,what is the best bounday condition for outlet?
if it's pressure outlet, so what about pressure gauge value?

 September 11, 2012, 22:22 #7 New Member   Join Date: Dec 2011 Posts: 29 Rep Power: 5 Hi, How do I modify my gambit drawing so that the air can be included above the reactor? If I have an open shell reactor how should I do? Thanks!

 January 18, 2015, 06:48 #8 New Member   Omar Osama Mohamed Join Date: Nov 2014 Posts: 21 Rep Power: 3 Hi all I am sorry but When I searched to model my free surface i found only Open channel flow which is horizontal how to define it as vertical ? Also what if i don't know my free surface dimensions I am modeling falling water film

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