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Old   July 30, 2009, 17:03
Question Flamelet model ,question :
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Its possible to work with FLAMELET MODEL in a premixed air/gas ? im simulating a combustion chamber(tubular) of a turbine.

which combustion model do you recommend me for simulate a combustion chamber (tubular) from a turbine Hitachi 24kW.?

thanks very much
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Old   July 30, 2009, 20:12
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Hi,

Flamelet model can be used for modeling premixed and partially premixed combustion as far as I know. However, the model is included as a submodel in CFX (as in V11.0) which you can use with the BVM/TFC model and Laminar flamelet with PDF model. This is explained in the help files in CFX.

You may need to use CFX-RIF to generate your own fluid model which require you to have a separate license. Otherwise you may have to rely on predefined models that comes with CFX.

Refer to the combustor modeling in CFX tutorial, in which they used flamelet model for premixed combustion.
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Old   July 30, 2009, 22:30
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the version that im using its cfx 10, and i was done the "combustion and radiation" tutorial ,in that tutorial uses the flamelet model and discrete transfer model(for radiation) ,but its a difussion flame(oxider and fuel stream enter separatly).

but i really dont know if exist some tutorial for the implementation of flamelet with premixed flames or partially premixed flames? and i dont know if CFX 10 work with this?

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Old   July 31, 2009, 01:46
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I do not know how it goes with CFX V10 as I have only experience with V11. However, the V11 is now obsolete with the introduction of V12, though will take some time to change over to V12.

The BVM model can be used for premixed and partially premixed combustion modeling. The combustor simulation using BVM, from what I understand, is shown for partially premixed combustion problem. The reaction progress variable can be hopefully used to control the mixture concentration in any domain during the turbulent simulation.

"mixing of the fuel and oxidant is represented by the mixture fraction, which can be seen as a normalized equivalence ratio. The location of the premixed flame front is determined by a reaction progress variable, where the turbulent burning velocity is used as an input parameter" (ref http://www.esss.com.br/pdf/CFXRCS.pdf)

I'm also in the learning procedure of premixed combustion. These are just my views. However, you can find something useful from the CFX help for BVM modelling.
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Last edited by geothokar; July 31, 2009 at 02:25.
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Old   July 31, 2009, 05:41
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thanks you very very much for your help,im in the learning of premixed moldel too,this is a long way to learn.

thanks again,im gona see the combustion model that you tell me.

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Old   August 21, 2009, 14:53
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hi...
i m also doing my phd on flammability limits ..... for that also i m working on premixed combustion .... i m having cfx 11 & 12 ...but i m bit confused how to apply Burning Velocity Model (BVM) and Laminar Flamelet with PDF models ...
kindly suggest me some method to apply.......

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Old   August 21, 2009, 19:55
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Hi,

Its better if you can tell where you are stuck, what is the problem now you are having with the model.

Also, if you can, brief your kind of application. For some cases EDM can be a better choice than BVM/LFC

Also, even if you have both CFX 11 & 12, you may not be encouraged with the performance of BVM model as the CFX comes with two default FLL models only, and so if you need to use a new mixture config, you should have CFX-RIF that comes as a separate license.
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Old   August 25, 2009, 13:02
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thanks for replying....
actually i m doing work on flammability limits...
in this the combustion model is spark ignited...
and i m not having any idea how to define spark in the cfx...
can u give me some guidance for that...
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Old   August 25, 2009, 18:53
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if u r using BVM,

for spark ignition to work, u shuld setup the following factors: spark kernel location, spark energy, energy coefficient, time duration for spark.

all there settings wil get activatd 1nce u choose BVM as comb. model.

& to get the bvm model activatd u shuld select FLL mixtre 1st in the material list and reaction list.

I wuld suggest to go with methane-air mixture.

also is imp. to initialize all parametrs in simulation with sensible values. otrwise everythng wil go crap!!!

if u hav plnty of tym to finish the work u r doing, u'll learn al the abov said things with experience.

if u r stil in starting stage, don't rush 2 get the comb. model. read more articles. get mor idea abt. hw comb. model works. it wil help u. am telng bcoz i hav 1st hand experience with dis kind of modeling.

gud luck
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Old   August 26, 2009, 13:10
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thank you very much for your kind help .....

regards
samip
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Old   September 7, 2009, 13:02
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hi....
as u suggest i did lot s of r & d on BVM/TFC model......
can v find a flame velocity.????/
as per astm std if the flame is reached on the top of 1.8m hight in 50cm tube thn the flame is flammable else not.............
i tried to solve this prob using cfx 11
but getting a error of domain overflow......
how to overcome 4m this........
as in this prob model is spark ignited 4m bottom and top of a cylinder should be closed.......
how to define this type of b c in cfx ........
can any one give me the suggestion
thanks regards
samip shah
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Old   September 23, 2009, 05:37
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im studing diffusion laminar flames before work directly with the flamelet model of ansys ,and i have a question:

i have understand that the difussion flames can be split in two problems:
1.-)mixing problem
2.-) a flame structure problem

am i right?..but..the flamelet model of ansys works with fast chemistry(equilibrium wk=0) but with irreversible/reversible/frozen chemistry?
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Old   September 24, 2009, 07:29
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The flamelet generator is based on finite rate chemistry. It calculates laminar stretched flames. The "laminar" flamelet model for turbulent flames assumes that the laminar stretch can be correlated to the turbulent. As this is more a theory question, check the books of Peters or Warnatz
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Old   September 24, 2009, 08:05
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thanks very much! ...my last question....flamelet model its a model who works with irreversible o reversible chemistry?

and what information its in the libraries of flamelets?

thanks very vey much
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Old   September 25, 2009, 16:24
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The flamelet generator is based on complete reaction mechanism with forward and backward reaction. So it is reversible, in the flamelet generator.

The 3D-CFD-solver does not calculate chemical reaction rate when the laminar flamelet model is used. The composition depends on mixture and turbulence, not on chemical kinetics. For practical case I suppose once the fluid has reached chemical equilibrium it will move along the equilibrium line.

Please read the combustion theory books for more details. (It is not CFX specific)
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Old   September 26, 2009, 03:19
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thanks very much for your help ,im studing with the book
theorical and numerical combustion from thierry poinsot-denis veynante

best regards
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