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-   -   how to apply VOF in a tank??? (http://www.cfd-online.com/Forums/cfx/24918-how-apply-vof-tank.html)

HAYATE December 13, 2007 03:22

how to apply VOF in a tank???
 
hello

i am trying to create a transient analysis of a tank that has 50% water and 50% air and a rotation of the tank about 30 decreas. and i would like to see only the surface of the water and how it is sloshing. i create the mesh (a cyllinder) and also read the tutorial but i have some question....

1) can i give all surfaces as a wall??? the tutorial describes only with inlet and outlets.

2) how to apply vof ? as the tutorial but i should change the high?

3) and last one ... any idea/???

best regards hayate

Glenn Horrocks December 13, 2007 17:09

Re: how to apply VOF in a tank???
 
Hi,

This should be a straight forward free surface simulation. The tutorials show how this is done, and you probably will be assisted by using the new multiphase coupled solver.

Your questions: 1) Yes. Remember that you probably will need something (eg an opening with a defined pressure) to allow the air to "breathe". 2) The free surface flow over a bump shows how to set it up

Glenn Horrocks

HAYATE December 14, 2007 08:53

Re: how to apply VOF in a tank???
 
HELLO GLENN

i read the tutorial 1000 times and i have try to create the simulation as the tutorial describes, the first thing that i would like to know is : how can i change the expressions? to say the software that there is the level of the water... also shall i put an input with 0 m/s and out put with a pressure 1 bar as the nature works? every time i get as results air and water sprayd everywhere....

any idea???

thanks in advance

cheeku December 14, 2007 09:03

Re: how to apply VOF in a tank???
 
hi

i have same problem as yours, but i want 2 c mixing of 4 different non reacting fluids, can u tell me how did u give position to air and water

HAYATE December 14, 2007 10:22

Re: how to apply VOF in a tank???
 
thats the easy part,

if you read the tutorial you will unterstand how to give the volume of the tank for each fluid, the problem is that something is not correct and the software unterstand the volumes wrong, i just want to have the water and the air , nothing else, on a transient analysis , and the walls will be interfacing with ansys so i will see the tank forces due to the tank rotation and the sloshing of the water, thats all.,

the only problem in that the software can not unterstand where is the water and where the air,

i figure to put an inlet with 0 velocity and a out with atmosphere pressure, but i did not finish that yet......

i will write you if i will do that correct.

thanks a lot

cheeku December 14, 2007 11:09

Re: how to apply VOF in a tank???
 
r u talking about free surface flow over a bump? Isint there a way with out expression. what will be the expression if tank is filled with 4 liquids in equal volume, the heaviest being at the bottom.

any ways good luck 4 your simulation, keep us inform about your progress

HAYATE December 14, 2007 11:29

Re: how to apply VOF in a tank???
 
i am talking about a cyllindricaly tank which is 50% with water and 50% with air, no inlet no outlet, just tank water air, i can not do that ....... and i am looking a solution....

thanks in advance

UnderwaterAlex December 14, 2007 11:51

Re: how to apply VOF in a tank???
 
Hi Hayate,

I am not exactly sure what problem you are having, but I'll offer some tips and maybe one of those will assist you. The air and water fractions should be input as the initial conditions to the simulation, using a step function similar to the tutorial. If the box is enclosed, you will need to put a small opening bc at the top (or far away from the flow) with a pressure boundary condition, otherwise the solver will have difficulties since there is no pressure information in the wall boundaries (this what Glenn was referring to as "breathing"). The water should have an initial hydrostatic pressure distribution, again following the example in the free surface tutorial. You'll want to make sure buoyancy is turned on and use the density of air as the reference density. From my experience, you should try getting a homogeneous two phase flow simulation working first, but if you are doing a true sloshing problem then there will be entrainment and you will probably need an inhomogeneous treatment eventually.

Best of luck,

-Alex

HAYATE December 14, 2007 11:59

Re: how to apply VOF in a tank???
 
underwater alex,

i just understand what glenn and you are saying, i did that and works fine, the solver understand the water and the air, the problem was that i put referance of water and not the air.....

ok..... well something else....... if i want to make a cube to swimm in the water i should create the solid as mesh or just put a wall boundary???

thanksssssssssss

you save me....

xujj December 15, 2007 23:01

Re: how to apply VOF in a tank???
 
I learn a lot from this, i will simulate single bubble in a liquid, I think that the bubble should be set dispersed phase, but the techinal support said that the single bubble should be set continuous phase,anyone gives me a suggestion? and the particle model or free surface model should be used in interface transfer? thanks in advance!


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