Combustion modelling

Prateek garg · December 29, 2012, 10:43

Hi Friends,

I am trying to model detonation, can someone suggest that which model is better out of Finite rate chemistry, eddy dissipation or combined finite rate and eddy disspation??
i have gone through the modelling guide but couldn't find any thing that support detonation.
Also, I wan to know that while defining reaction if I use combustion model as Finite rate chemistry and eddy dissipation and use only Finite rate chemistry in fluid Models tab of Domain. which model it will take to model reaction??

ghorrocks · December 30, 2012, 06:27

This sounds like a literature review is required. Time for you to head to the library.

Which model is best for you depends on many things, including the results you intend to get out, how accurate you need to be and your knowledge of combustion physics and modelling.

Prateek garg · December 30, 2012, 10:59

Hi Glenn,

Thanks for being there and solving my problems from miles apart.
I will do the literature survey, I also want to know if while defining reaction, I am specifying combustion model as finite rate chemistry and eddy dissipation, there is also an option in domain for choosing combustion model, if I choose there finite rate chemistry then which model will CFX used to model combustion??

ghorrocks · December 30, 2012, 15:14

I not an expert in combustion, but I know CFX supports simple models based on eddy dissipation and more advanced models using flamelet libraries (RIF).

Prateek garg · December 31, 2012, 11:27

OK,
I also have one more doubt, I hope you can help on this.
As i told you am trying to model detonation and I am done with mixing of tube with fluid, now I want to use these results (.res) as input file for next step i.e. ignition. For ignition I am using a small volume patched with high temperature and pressure (5 atm and 2000K )and another bigger volume i.e rest of the tube with 300K and 1 atm. but the problem is after i start the run i saw that volume is not patched with HIGH temp and pressure (as I check at 0 time step). I am thinking that its taking the value of temperature and pressure from results file, but then in that case How can i patch this domain?? What could be the possible reason??

Possa · December 31, 2012, 11:57

Dear Prateek,

CFX combustion models are quite simple for modeling detonation and ignition with accuracy I believe.

If you are focusing in the combustion problem and want results like flame speed, minor species, etc, then I would suggest you to use the software CHEMKIN (from reaction design). This software is for chemical reactions and is quite good for dealing with reactors.
But keep in mind that it is really different from CFD softwares, it is a chemical reactions modeler.
Combustion models in CFX are good when you want to estimate thermal results from a global combustion problem like wall temperatures or heat fluxes on combustion chambers but it is not good for estimations on actual combustion experiments.

I hope that helps,

Regards,
Possa.

December 29, 2012, 10:43	Combustion modelling	#1
Prateek garg Member Prateek Join Date: Mar 2012 Location: Bangalore Posts: 32 Rep Power: 14	Hi Friends, I am trying to model detonation, can someone suggest that which model is better out of Finite rate chemistry, eddy dissipation or combined finite rate and eddy disspation?? i have gone through the modelling guide but couldn't find any thing that support detonation. Also, I wan to know that while defining reaction if I use combustion model as Finite rate chemistry and eddy dissipation and use only Finite rate chemistry in fluid Models tab of Domain. which model it will take to model reaction??

December 30, 2012, 10:59	Combustion modelling	#3
Prateek garg Member Prateek Join Date: Mar 2012 Location: Bangalore Posts: 32 Rep Power: 14	Hi Glenn, Thanks for being there and solving my problems from miles apart. I will do the literature survey, I also want to know if while defining reaction, I am specifying combustion model as finite rate chemistry and eddy dissipation, there is also an option in domain for choosing combustion model, if I choose there finite rate chemistry then which model will CFX used to model combustion??

December 31, 2012, 11:27	Combustion modelling	#5
Prateek garg Member Prateek Join Date: Mar 2012 Location: Bangalore Posts: 32 Rep Power: 14	OK, I also have one more doubt, I hope you can help on this. As i told you am trying to model detonation and I am done with mixing of tube with fluid, now I want to use these results (.res) as input file for next step i.e. ignition. For ignition I am using a small volume patched with high temperature and pressure (5 atm and 2000K )and another bigger volume i.e rest of the tube with 300K and 1 atm. but the problem is after i start the run i saw that volume is not patched with HIGH temp and pressure (as I check at 0 time step). I am thinking that its taking the value of temperature and pressure from results file, but then in that case How can i patch this domain?? What could be the possible reason??

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December 30, 2012, 06:27		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,696 Rep Power: 143	This sounds like a literature review is required. Time for you to head to the library. Which model is best for you depends on many things, including the results you intend to get out, how accurate you need to be and your knowledge of combustion physics and modelling.

December 30, 2012, 15:14		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,696 Rep Power: 143	I not an expert in combustion, but I know CFX supports simple models based on eddy dissipation and more advanced models using flamelet libraries (RIF).

December 31, 2012, 11:57		#6
Possa New Member Talita Possamai Join Date: Sep 2012 Posts: 23 Rep Power: 13	Dear Prateek, CFX combustion models are quite simple for modeling detonation and ignition with accuracy I believe. If you are focusing in the combustion problem and want results like flame speed, minor species, etc, then I would suggest you to use the software CHEMKIN (from reaction design). This software is for chemical reactions and is quite good for dealing with reactors. But keep in mind that it is really different from CFD softwares, it is a chemical reactions modeler. Combustion models in CFX are good when you want to estimate thermal results from a global combustion problem like wall temperatures or heat fluxes on combustion chambers but it is not good for estimations on actual combustion experiments. I hope that helps, Regards, Possa.