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-   -   Diffusion Flames with Flamelet model ,little question. (http://www.cfd-online.com/Forums/main/68543-diffusion-flames-flamelet-model-little-question.html)

AdidaKK September 23, 2009 10:00

Diffusion Flames with Flamelet model ,little question.
 
im studyn the theory of diffusion flames before and i understand thats one of the assumptions for the introduction of mixture fraction it is to decouples the diffusion flame computations in two problems:

1)Mixing problem : determine the field of the mixture fraction z(xi,t) as function of spatial coordinates xi and time t.

2)A flame structure problem: where the links between flame variables ( mass fraction Yk(z),T(z) ) and z are use to construct all flames variables.

in other words

z(xi,t)---->(scalar dissipation rate field)---->T(z) ; Yk(z)---->solution of the full problem T(xi,t) ; Yk(xj,t).


my question its , the flamelet model ,how its works with this? the libraries has wich information? , what its the 2 scalar equation who use flamelets?
i hope someone cane help me.

best regards
Mauricio:D

AdidaKK September 24, 2009 10:26

XDD..the two scalar equations its Temperature and mas fraction in function of the mixture fraction.

but the libraries ,wich information contains?

and my last question,the flamelet model its a model based on finite rate chemistry(non equilibrium) but irreversible o reversible chemestry?:eek:

esozer October 17, 2009 10:41

In its basic form, you don't solve the species mass fraction equations or the energy equations

You solve: continuity, momentum, mixture fraction (Z) and mixture fraction variance (Zvar) equations.

Then you (typically) model the scalar dissipation rate (chi) using the mixture fraction variance and k and epsilon (or omega) assuming you are using RANS.

Flamelet table will work as:

Z, Zvar, Chi -> rho, mu, diffusivity (for Z), T, Yi

The last two are only needed for post processing.

Reversible reactions are OK. But with flamelet model, chemistry is assumed fast (not infinitely fast though)

Check out: Peters, N., “Turbulent Combustion”, Cambridge University Press, 2000.

Hope this answers your question.

AdidaKK October 17, 2009 10:47

thanksssssssss very veryyyyyy much for your help! ,one more thing ,can you visit the ansys cfx forum and see the two first post? both are mine with 2 little question about flamelet ,can you give me your opinion, please?

thankss very veryyy much for your answer
best regards

esozer October 17, 2009 11:00

1 Attachment(s)
I think I already answered those questions.

You solve: Z and Zvar equations
You model: chi

Yes, flamelet model is for finite rate but fast chemistry.

Flamelet table is usually a 3D loop-up table with Z,Zvar and Chi as independent variables and rho, mu, diffusivity, T, Y, .... (can contain more depending on implementation).

See the attached chart.

Note: flamelet model is not unique and many variations are there (to solve another equation for chi, etc...) What I am explaining is the most basic form.

AdidaKK October 17, 2009 11:09

ohhhhhhh THANKKKKKKKKKKKKKKKKKKKKKKS VERY MUCH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! IM SO HAPPY RIGHT NOW!!!

last question..that image you attach..its from the book that you recommend me? peters "turbulent combustion" cambrige 2000?



THANKS VERY VERYYYYY MUCH AGAIN! now i can sleep!:D:D:D:D

esozer October 17, 2009 11:27

No problem. The image is not from the book. It's something I prepared myself.

AdidaKK October 17, 2009 11:34

ohh i see ,andd...thats material it is avaible for the public? or its secret property?:D

esozer October 17, 2009 11:37

It's from my dissertation which will be available in a few weeks

AdidaKK October 17, 2009 11:40

exellent ,do you will post here your presentation?
im gona be waiting ...exellent job
best regards

AdidaKK November 3, 2009 02:03

uhm...i read the theory modelling of ansys cfx ,and one of the assumptions for flamelet model its was lewis number equal to unity, my question is: the species heat capacities are equal and constant too? (Cpk=Cp)

thanks very much

AdidaKK November 3, 2009 03:01

ohh and one more, flamelet model its single step chemistry? or multi step?

thanks veryy much


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