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star123 January 25, 2006 11:02

vof tank emptying
How to use the vof and set the BC to simulate the tank? Thanks a lot!

edi January 25, 2006 11:30

Re: vof tank emptying
Very briefly:

- Patch the initial fill level of liquid;

- Set the outlet as a velocity boundary (remember to set volume of fraction of liquid=1 in the BC panel);

- There must be also a pressure inlet for the gaseous phase (or a reservoir).

Let know if you need more hints.


PS if you want to catch nice draining vortexes, pay A LOT attention to your mesh.

star123 January 25, 2006 18:07

Re: vof tank emptying
it helps a lot. thx one more question, I can not fix the outlet velcity, because during the tapping, the lower bath level will give the lower outlet velocity also. If it is possible to set pressure BC or others?

edi January 26, 2006 04:44

Re: vof tank emptying
In this case you can use two pressure boundaries, but be very careful in setting the pressure values relative to the operating pressure, the backflow volume fraction and where to place this pressure boundaries (much better where only one phase will enter/go out of them throughout your simulation).

Hope this helps & good luck,


star123 January 26, 2006 04:59

Re: vof tank emptying
i put the top surface of tank pressure 0, and bottom outlet pressure also 0, then after 1 iteration step, converged, and every variable becomes 0.

How to put this kind of BC?

Thanks a lot for your suggestion

edi January 26, 2006 05:13

Re: vof tank emptying
Sounds like no flow is occurring.

If I understood right the two basins are at different heights and you want to study the flow between them driven by the gravity force, is it correct?

Some things to check:

-first of all enable gravity;

-patch the initial location of fluid (of course it must not be in an equilibrium position);

-I think you can set the two pressure boundaries at the same value, but they must be quite above the location of the free surfaces, I guess...never tried.

Good luck


star123 January 26, 2006 05:37

Re: vof tank emptying
you understand it correctly.

I tried pressure bc 0 at the top of tank, about 1m above initial water free surface, and pressure bc 0 at the bottom of tapping pipe, also give the gravity.

but no solution. I am a little bit confuse how to do that simulation. thx again

edi January 26, 2006 06:14

Re: vof tank emptying
Ok, I've got it. This problem was making me curious, moreover, it has to do with my work, so I builded up a little 2d model of two square basins at different heights united at the bottom with a little duct (sorry for my english, hope I'm making myself clear). One basin is initially partially filled with liquid and the other is empty. The ceiling of the first basin is a pressure inlet boundary with p=0 and the other is a pressure outlet BC at p=0 too. I started an unsteady simulation and the liquid is effectively flowing from one tank to I don't think it's a BC choice item, maybe it has to do with the position of the boundary or more probably with another item, you have to go more into details...

Good luck


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