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VOF BC not compatible?

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Old   November 19, 2014, 14:54
Default VOF BC not compatible?
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Hi everyone!
I am simulating a free falling film of water, but Fluent does not agree with my settings.
I am using VOF with implicit volume fraction scheme, open channel flow with implicit body force.
I use mass-flow inlet with only water, and the outlet at outflow.


Edit: By testing switching off open channel flow I no longer get the warning.
However, the fluent theory manual states that I in fact can use mass-inlet/outflow with open channel flow enabled.

Please help?
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Old   November 21, 2014, 15:44
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hi
use mass flow inlet as inlet boundry condition and pressure outlet as outlet
set the mass flow of air at inlet zero
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Old   November 21, 2014, 18:36
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Hi Herrolsen,

It sounds like you have a supercriticality in your simulation, so the free surface heights at both the top and bottom reservoirs will not be implicit in the problem definition, and therefore you must specify both boundary conditions.

The actual condition depends on the problem. If you're simulating a fixed mass flow condition, obviously use that particular bc, but if you are simulating near-infinate length reservoirs, then pressure bcs with hydrostatic profiles are more applicable.

Good Luck

Stu
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Old   November 24, 2014, 13:14
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Quote:
Originally Posted by HyperNova View Post
hi
use mass flow inlet as inlet boundry condition and pressure outlet as outlet
set the mass flow of air at inlet zero
But it specifically says that those BCs are not compatible?
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Old   November 24, 2014, 14:08
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Quote:
Originally Posted by stuart23 View Post
Hi Herrolsen,

It sounds like you have a supercriticality in your simulation, so the free surface heights at both the top and bottom reservoirs will not be implicit in the problem definition, and therefore you must specify both boundary conditions.

The actual condition depends on the problem. If you're simulating a fixed mass flow condition, obviously use that particular bc, but if you are simulating near-infinate length reservoirs, then pressure bcs with hydrostatic profiles are more applicable.

Good Luck

Stu
Thanks man!
I am simulating a fixed mass flow condition, so that seemed like the most appropriate BC to use. Just found it weird that the manual and program contradicts itself. Then I'm blank again, anyone have an idea of why I can't use these settings together?
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Old   November 24, 2014, 23:31
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Quote:
Originally Posted by HyperNova View Post
hi
use mass flow inlet as inlet boundry condition and pressure outlet as outlet
set the mass flow of air at inlet zero
DUDE ! I misread the manual, thank you sooo much!!!!
It seems to be working now. Lots of love HyperNova!
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Old   November 25, 2014, 11:56
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Quote:
Originally Posted by herrolsen View Post
DUDE ! I misread the manual, thank you sooo much!!!!
It seems to be working now. Lots of love HyperNova!
i am happy to hear that you managed to solve your problem , good luck friend
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Old   November 25, 2014, 11:58
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Thank you very much! It seems to be stable now. I still don't understand why I cant use outflow though :P
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Old   November 26, 2014, 04:02
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Quote:
Originally Posted by herrolsen View Post
Thank you very much! It seems to be stable now. I still don't understand why I cant use outflow though :P
you can locate outflow boundry condition where the flow is fully developed otherwise the result will be wrong , by the way is this your university project ? where do u study ?
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Old   November 26, 2014, 13:51
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That explains why it was unstable, thanks again HyperNova! Yes it is I study in Sweden!
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Old   November 26, 2014, 16:53
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your welcome my friend ,by the way i study in iran, MSc in hydraulics engineering , i hope you more success and luck , forgive my bad english
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