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-   -   Finite-Rate/Eddy-Dissipation doesn't work! (http://www.cfd-online.com/Forums/fluent/71418-finite-rate-eddy-dissipation-doesnt-work.html)

jiahang December 31, 2009 20:09

Finite-Rate/Eddy-Dissipation doesn't work!
 
Hi there:

I am setting up a very simple case: injecting CO into air to achieve the combustion. The carbon monoxide air is my mixture. First I chose Finite-Rate/Eddy-Dissipation as my combustion model, there is no combustion at all even after I initialized my case with 2000K!

Later I only use Eddy Dissipation model, then the combustion comes.

Does someone know why I can't use the first model? I find other people did similar thing with this model, so I assume that should work for me too.

Thank you for your any suggestion so much! Happy new year to you!

gsyuan December 31, 2009 23:06

you may try initialize----patch give a high temperature
 
you may try initialize----patch give a high temperature

jiahang January 1, 2010 19:20

Thank you gsyuan!
 
Hi gsyuan:

Thank you for answering my question. I did initialization already with 2000K, but nothing changes.

My kinetic/ED model's set up of BC conditions is exactly as the same as the ones of ED model. Since I can see the combustion in ED model, I think I may make a very basic mistake somewhere. I don't know if the former model has different requirements on the case?

I hope I explain my problem well to you.

Thank you again and wish you a good new year!

jiahang

pghoseju July 25, 2012 04:59

The same problem I am facing too. Only with ED model it is working but FR/ED it does not work. Help me.......

NormalVector July 25, 2012 18:38

Is your simulation transient? I'm having the same trouble with my transient simulation.

eng_s_sadeghi July 25, 2012 22:59

Ansys Fluent have enabled spark model for ignitions. Try them. Ooh, I forgot something, you should also patch a very small amount of species (reactants and products) around the spark point to could start ignition.

pghoseju July 26, 2012 06:49

thank you for your suggestion. I am using steady flow. I have given pach 1500 K near ahead the nozzle tip. and I have tried with paching to the whole body at temp. 1500k. I pached the products only on the whole domain.

Now my problem is that when I am running with FR/ED, it is running and I checked the results (temp, species mass fraction etc.) after few iteration(50 iteration) , It shows the results. but when I left it for more iteration(600 iteration), the resulted temperature is now the cold flow temperature.

some time it shows the flame (maximum temp.)at the combustor exit. which is not right. actually what may be the problem?

pghoseju August 2, 2012 07:45

No my problem is steady one. Now my problem is solved. It is working now. But problem is that, it shows the maximum

pghoseju August 8, 2012 03:48

Quote:

Originally Posted by jiahang (Post 241206)
Hi there:

I am setting up a very simple case: injecting CO into air to achieve the combustion. The carbon monoxide air is my mixture. First I chose Finite-Rate/Eddy-Dissipation as my combustion model, there is no combustion at all even after I initialized my case with 2000K!

Later I only use Eddy Dissipation model, then the combustion comes.

Does someone know why I can't use the first model? I find other people did similar thing with this model, so I assume that should work for me too.

Thank you for your any suggestion so much! Happy new year to you!

I can help you. but first of all you have to say.
1. whether you are using spray combustion or simple gas combustion?

Jenny_W March 11, 2013 13:54

Hi,
I am modelling compressible non-combustion reacting flow in FLUENT. I am using the species transport laminar finite rate model but there is no reaction.

I have initialized and patched a region of high temperature and high reactant concentration near the inlet. I also tried increasing the inlet temperature but nothing works. I still have no reaction.

If anyone can know what may have gone wrong, please give me some suggestion.
Thank you,
Jenny

msaeedsadeghi March 12, 2013 01:42

Quote:

Originally Posted by Jenny_W (Post 413179)
Hi,
I am modelling compressible non-combustion reacting flow in FLUENT. I am using the species transport laminar finite rate model but there is no reaction.

I have initialized and patched a region of high temperature and high reactant concentration near the inlet. I also tried increasing the inlet temperature but nothing works. I still have no reaction.

If anyone can know what may have gone wrong, please give me some suggestion.
Thank you,
Jenny

I always patch both reactants and products in whole domain but in a small amount. Also patch reasonable temperature on a proper location.

Jenny_W March 12, 2013 04:46

Hi Saeed,
I will do that. Thank you very much for your help.
Regards,
Jenny

Jenny_W March 13, 2013 16:08

Hi Saeed,
I have tried patching the whole domain with reactions, products and patch a region with high temperature and it's still not working. Would you please suggest what else I could try?
Thank you,
Jenny

pghoseju March 15, 2013 09:39

Hello Jenny.
1. what is your fuel?
2. whether it is liquid fuel spray combustion or gaseous fuel combustion?

Any way you can use an option "relax to chemical equlibrium".
where you have to use ''chemistry calculation per iteration is =10''
''aggressive factor =0.5''
Remeber
In ISAT table you have to select the fuel.
and before running you have to clear the Isat table.

after paching you will run the programme for let say 300 itr.
again patch the computational domain like early case.
again run it without initialize it.
then see what happen.............

pghoseju March 15, 2013 09:40

But at last I will suggest you to non-premixed model, if your problem is non premixed

Jenny_W March 15, 2013 11:25

Hi Prakash,

Thank you very much for your suggestions. I will try to do as you recommend.

1. I do not use fuel. I am modelling non-combusting atmospheric chemical reaction. Since my reaction is not available in FLUENT, I have to import the reaction in CHEMKIN format into fluent.

2.The is gaseous reaction.

3. I tried using non-premixed combustion model with steady flamelet chemistry. After importing CHEMKIN mechanism and thermodynamic database files, I failed to calculate flamelets.

FLUENT exit and reported the error "Single flamelet extinguished Try again with lower Scalar Dissipation". I tried lowering the scalar dissipation but it didn't work. When I tried activating "Liquid Micro-mixing", the error was gone but i think that this option is not appropriate for my case as it is a gaseous reaction.

Can non-premixed combustion model be used to simulate non-combusting gaseous chemical reaction?

Thank you,
Jenny

WJXu April 16, 2014 11:51

Quote:

Originally Posted by pghoseju (Post 375028)
No my problem is steady one. Now my problem is solved. It is working now. But problem is that, it shows the maximum

Hi, I am facing the same problem now. I am simulating the gas combustion, CH4/Air from different inlets. ED model reacts, while FR/ED doesn't. How did you resolve your problem? Endless thanks, please help me.

hazwani fatihah April 13, 2015 04:40

Hi guys,

My simulation was transient. I used species transport laminar finite rate model for methane/air combustion. I got very high velocity, it was wrong. Am I picking the right model? Should I used FR/ED for my model?

Id appreciate if anybody could help me out on this.

Thank you

sanjeetlimbu April 24, 2015 22:28

3 Attachment(s)
Dear Sir

I am trying to do autoignition for mixture heptane/N2/O2/AR: 0.562/58/30/10 mole fraction ratio

But unable to do it by any method .. I set the initial T=766K and Presuree= 14.1 bar

1. I tried the laminar rate- it showing error : flat Temp profile



Please guide me how to get autoignition by laminar ... I am in trouble

sanjeetlimbu April 25, 2015 01:13

After trying in step to off volumetric calculation and run again with the all equations set.
I am getting error after some iteration as


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