how to set the levels of two fluids with the vof

[Efes88]

Hello! I have a fluent problem....I have to study the dynamics of the free fur of a fluid in a tub moved by a piston, in the tub is there water up to a certain height and then air over how do I set on fluent the height occupied by the water?

 

[Onda]

I used cfx and not fluent, but I think you could use the same.
you have to use a step function to set the vof.
step is worth 1 if positive or 0 if negative or nothing.
impose the step on the height of the free fur and if you have to generate a wave you will change in height according to the wave motion in time.
then define for your inlet that the inlet fluid composed of the two air and water fluids has mass equal to the step(z) function for air and -step(z) for water.
in the case of transient with wave becomes step(z(t)).

for example if the free fur is located at 2000mm from 0 of the model the air volume becomes:
vof aria=step(z-2000) and
vofh2o=step(2000-z).
In this way you define the composition of the inlet fluid.

 

[Efes88]

Thanks for the answer, however, more precisely in my case the wave motion I do not know it... I must observe it after I have imposed the piston motion (which is then a face of the tub) so I simply have to indicate the water level in the initial condition. I'm trying with patch after making initialization by putting volume fraction (water)=1 to the area created on gambit where the water should be present but I'm afraid that this is just a verification.... about the step function... is it inside the program or should I create it? I would be very pleased if I explained + in the detail what is... thank you very much!!

 

[sail]

Thanks for the answer, however, more precisely in my case the wave motion I do not know it... I must observe it after I have imposed the piston motion (which is then a face of the tub) so I simply have to indicate the water level in the initial condition. I'm trying with patch after making initialization by putting volume fraction (water)=1 to the area created on gambit where the water should be present but I'm afraid that this is just a verification.... about the step function... is it inside the program or should I create it? I would be very pleased if I explained + in the detail what is... thank you very much!!

http://mox.polimi.it/it/informazioni/personale/viewpers.php?id=1&en=&tesi=onin the last tense or in that of simone square you should find the necessary udfs to define the initial conditions you need.

 

[Efes88]

I think I solved the problem by patching after initialization. ..in fact after doing some iterations the trend of the contours of the volum fraction of the water phase give me a clear distinction between the two phases and the free fur begins to move!! wow...only that now I have the problem that from the preview of the mesh motion I get a negative voiume after about 3 s (with consequent block of the simulation when I arrive at that time) I would like to know if I had to set the elastic smoothing via text command since the mesh is rectangular. . That's the only problem I know how to do. .