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Finite-Rate/Eddy-Dissipation doesn't work!

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Old   December 31, 2009, 20:09
Default Finite-Rate/Eddy-Dissipation doesn't work!
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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!
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Old   December 31, 2009, 23:06
Default you may try initialize----patch give a high temperature
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you may try initialize----patch give a high temperature
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Old   January 1, 2010, 19:20
Default Thank you gsyuan!
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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

Last edited by jiahang; January 1, 2010 at 21:43.
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Old   July 25, 2012, 04:59
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The same problem I am facing too. Only with ED model it is working but FR/ED it does not work. Help me.......
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Old   July 25, 2012, 18:38
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Is your simulation transient? I'm having the same trouble with my transient simulation.
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Old   July 25, 2012, 22:59
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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.
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Old   July 26, 2012, 06:49
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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?
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Old   August 2, 2012, 07:45
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No my problem is steady one. Now my problem is solved. It is working now. But problem is that, it shows the maximum
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Old   August 8, 2012, 03:48
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Quote:
Originally Posted by jiahang View Post
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?
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Old   March 11, 2013, 13:54
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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
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Old   March 12, 2013, 01:42
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Quote:
Originally Posted by Jenny_W View Post
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.
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Old   March 12, 2013, 04:46
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Hi Saeed,
I will do that. Thank you very much for your help.
Regards,
Jenny
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Old   March 13, 2013, 16:08
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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
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Old   March 15, 2013, 09:39
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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.............
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Old   March 15, 2013, 09:40
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But at last I will suggest you to non-premixed model, if your problem is non premixed
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Old   March 15, 2013, 11:25
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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
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Old   April 16, 2014, 11:51
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Quote:
Originally Posted by pghoseju View Post
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.
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Old   April 13, 2015, 04:40
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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
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Old   April 24, 2015, 22:28
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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
Attached Images
File Type: jpg Laminarfinite-rate.jpg (50.4 KB, 9 views)
File Type: png initial.PNG (25.5 KB, 8 views)
File Type: jpg initial.jpg (55.7 KB, 6 views)
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Old   April 25, 2015, 01:13
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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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