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Partially Premixed Combustion

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Old   July 26, 2006, 08:57
Default At the risk of asking a really
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Ramiro Brito Willmersdorf
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At the risk of asking a really silly question...
(Remember: as Homer Simpson used to say -- "There are no stupid questions, just stupid people")

What exactly is considered partially premixed combustion in OpenFoam? "Partially Premixed" sounds like "partially pregnant"

I'm asking this because I'd like to know to which kind of problems XiFoam is applicable.

(BTW: I know what are premixed and non-premixed combustion, but I was under the impression this was an either/or thing.)

Many thanks!
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Old   July 26, 2006, 09:39
Default Hi Ramiro, which kind of comb
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Hi Ramiro,
which kind of combustion problem would you like to simulate?
Bye
Tommaso
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Old   July 26, 2006, 11:02
Default Hi Tommaso, Jet Fires, ie,
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Hi Tommaso,

Jet Fires, ie, (possibly very large) flames in an open environment, originated at a high speed gas leaks. Very non-premixed, I would think.
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Old   July 27, 2006, 02:25
Default I think it is partially-premix
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I think it is partially-premixed combustion, thus it might be better to use reactingFoam
bye
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Old   July 27, 2006, 14:53
Default Well, there you are, that's wh
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Well, there you are, that's why I'm asking.

I thought (and to be honest, still do think) that since the fuel and air are coming in separate streams, this would be non-premixed combustion.

I also thought that for partially premixed combustion there could be less expensive (than solving the full chemistry) models implemented in OpenFOAM, based on flamelet libraries, pdf's, etc. That's why I was curious about XiFoam.

Why do you thing reactingFoam would be more adequate?
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Old   July 27, 2006, 15:01
Default Non-premixed combustion (almos
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Non-premixed combustion (almost) never exists.
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Old   July 27, 2006, 15:10
Default Of course I meant "Why do you
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Of course I meant "Why do you think"
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Old   July 27, 2006, 15:28
Default Hello Joan, Yes, I understa
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Hello Joan,

Yes, I understand that, in reality, really non-premixed combustion is almost impossible, except on very controlled laminar counterflow experimental setups.

However, I was under the impression that there are very different approaches to numerical modeling of combustion when the fuel and oxidant come to a combustion "chamber" already mixed in the same stream, or when they come in different streams and are mixed in the combustion "chamber" by the combustion process itself. I thought (and, at the risk of sounding really stubborn, still do ) that this was what was meant by "premixed" and "non-premixed" combustion in the numerical combustion literature.
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Old   July 27, 2006, 16:18
Default You are perfectly right. T
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You are perfectly right.

The reality is that non-premixed models are unable to predict correctly the most important part of the `non-premixed flame': the impact of the premixing occuring into the chamber on the flame. Simply because there is no place for premixing in their formalism which is strictly non-premixed. This is a matter of fundamental hypothesis. Not a weakness of the models by themselves.

As a consequence the point of maximum heat release, where the flame is lifted, as well as anchoring cannot be addressed with these models. The critical part of the physics is missed. This is why partially-premixed models have been proposed.
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Old   July 28, 2006, 06:54
Default OK! I think I see the point
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OK!

I think I see the point perfectly now!

Many thanks!
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