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February 16, 2013, 13:31 |
OUTFLOW BC explanation in fluent
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#1 |
New Member
Debanjan Deep
Join Date: Mar 2009
Posts: 14
Rep Power: 17 |
I have a question regarding the mass flow rate during outflow boundary condition employed in FLuent. It requires a mass flow ratio in case of multiple outlets of Outflow BC.
I am wondering why this mass flow rate ratio is required to put in fluent since I believe fully developed flow is sufficient bc condition to satisfy NS equation. Am I right? In case of multiple outflow outlet bc, it is mandatory to put those mass flow weight ratio to get a perfect simulation result as I have experienced before. Can anyone explain this from NS equation using some easy scheme like FDM? I am new in this field so any help would be highly appreciated! Thanks, Debanjan |
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February 17, 2013, 09:28 |
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#2 |
Senior Member
Lefteris
Join Date: Oct 2011
Location: UK
Posts: 337
Rep Power: 15 |
It has to do with the conservation of mass. Since there are no sources or sinks, what comes in must go out. Thus, the sum of the mass leaving the domain must be equal to the mass entering the domain, regardless of the number of the inlets and outlets. In the case of multiple outlets you determine the portion of the flow that "uses" the one or the other outlet.
The fully developed flow you mentioned isn't a useful condition, actually it's not a BC at all. Best regards, Lefteris |
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February 18, 2013, 06:52 |
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#3 | |
Senior Member
andy
Join Date: May 2009
Posts: 270
Rep Power: 17 |
Quote:
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February 18, 2013, 09:51 |
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#4 |
Senior Member
Lefteris
Join Date: Oct 2011
Location: UK
Posts: 337
Rep Power: 15 |
You're absolutely right andy_ but as you said, for the specific problem they're not sufficient. Generally speaking though, these are the BC that should be used, you're right.
__________________
Lefteris |
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February 18, 2013, 11:01 |
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#5 |
New Member
Debanjan Deep
Join Date: Mar 2009
Posts: 14
Rep Power: 17 |
Well, my question here is why it is not sufficient for multiple outlets ? Can this be proved from NS equation point of view?
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