CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

Transient Turbulent Combustion.

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 16, 2017, 17:31
Default Transient Turbulent Combustion.
  #1
New Member
 
rajugsr
Join Date: Oct 2016
Location: India
Posts: 7
Rep Power: 5
gr135 is on a distinguished road
Hi everybody

I have been trying to run Combustion of Methane-air mixture using species transport eddy dissipation model. I happen to see rise in temperature to 2400 in steady state which is expected but in transient state I see no combustion in the flow or any trace of product species.

Is there something I am missing in transient combustion? I have learnt from other forum that in steady state solver sets many higher order and non-linear terms to zero which are time dependent that might be the reason why I see agreeable results. Can someone guide on how to simulate Transient combusting flows?
gr135 is offline   Reply With Quote

Old   April 17, 2017, 00:12
Default
  #2
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 3,571
Rep Power: 44
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Did you start your transient simulation from the steady results? Play a video (easy to say, harder to day) and watch what happens to the flame. Probably it couldn't stabilize and burnt out, much like lean blow-off.

Large time-steps in transient are also prone to blow off.
LuckyTran is offline   Reply With Quote

Old   April 17, 2017, 11:55
Default
  #3
New Member
 
rajugsr
Join Date: Oct 2016
Location: India
Posts: 7
Rep Power: 5
gr135 is on a distinguished road
Hi,

Thanks for the response

Not from results but I have run transient analysis with the same setup I have used for steady analysis. I see no flame in transient analysis nor do I see any production of CO2 and H20 at any point in the total flow time of 1 sec that verifies that there is no lean blow off I guess.

flow is not diverging even at time step of 0.01, that takes out large timestep out as probable reason.
gr135 is offline   Reply With Quote

Old   April 17, 2017, 18:00
Default
  #4
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 3,571
Rep Power: 44
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Yes but in your transient analysis you must have started with some initial condition. There should have been some sort of flame, or maybe you started with a cold-flow with an igniter.

A mixture of methane and air doesn't spontaneously ignite.

If there's no flame ever, then there won't be any flame ever. Combustion isn't spontaneous. Obviously if there's no flame you won't see any flame blow-out because there's no flame.
LuckyTran is offline   Reply With Quote

Old   April 18, 2017, 13:18
Default
  #5
New Member
 
rajugsr
Join Date: Oct 2016
Location: India
Posts: 7
Rep Power: 5
gr135 is on a distinguished road
Okay, does it mean that I should start with steady analysis for few iterations and then continue with transient analysis? But would that simulation give me a video on how the flow the flame is developing in the flow?

My reasoning: I have given air inlet above 1000 degrees which is higher than auto-ignition temperature of methane so I expected flame without any igniter.

Thank you for the response.
gr135 is offline   Reply With Quote

Old   April 18, 2017, 18:22
Default
  #6
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 3,571
Rep Power: 44
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
I'm not sure why it didn't ignite while above the autoignition temperature, but it's highly dependent on the combustion model. Some models just can't simulate any ignition events at all (i.e. flame speed models).

I would use the steady case and switch over to transient, since you are sure there is a flame in that case. Just check and make sure the flame doesn't get blown out.
LuckyTran is offline   Reply With Quote

Old   April 20, 2017, 14:32
Default
  #7
New Member
 
rajugsr
Join Date: Oct 2016
Location: India
Posts: 7
Rep Power: 5
gr135 is on a distinguished road
Yeah I have tried doing that. In fact I have run the same case in CFX and it worked well, observed stable flame in transient analysis.

I don't know if its the right place to ask the question and I have posted this in CFX forum but If you can help it would be pretty helpful.

I have been trying to simulate combusting flows using EDM and apply Electromagnetic model to it. I want to capture the effect of magnetic and electric fields on combusting flow field in a duct combustor. The ions generated in the flow due to chemical reactions and the high temperatures should be effected my the body forces and I intend to measure the field strengths required to effect the flow structures in the field.

I have tried to couple all the physics in comsol but I do not have the level of understanding required to do it in comsol.

I wanted to know if the same can be done in CFX activating EM model along with the flow. I am unable to find the electrical conductivity properties of reactants and products of the reaction that I want to simulate in order to see what the model does. (hydrogen- Air Mixture)

I did not understand which combustion model is the right pick as you say its highly dependent on the model we pick. I have learnt from tutorial that PDF Flamelet can generate information regarding the intermediate ions in the reactions but I do not have license for CFX RIF to generate PDF libraries? if there way I can find Pdf libraries in the internet for Hydrogen-air mixture.

So, Can it be done in CFX with EM model? Things I should try in sequence to be able to do order to do it? or softwares I should try to learn

Thank you for your time and valuable suggestions.
gr135 is offline   Reply With Quote

Old   April 24, 2017, 18:51
Default
  #8
New Member
 
rajugsr
Join Date: Oct 2016
Location: India
Posts: 7
Rep Power: 5
gr135 is on a distinguished road
Hey!

Anyone who can help me with aforementioned query?

Thank you for your response in advance.
gr135 is offline   Reply With Quote

Old   October 18, 2018, 10:24
Default
  #9
Member
 
Emerson
Join Date: May 2018
Posts: 33
Rep Power: 3
souza.emer is on a distinguished road
Quote:
Originally Posted by gr135 View Post
Hey!

Anyone who can help me with the aforementioned query?

Thank you for your response in advance.
Hey Gr135,

I'm trying to simulate a transient combustion too, with the reaction CO + 1/2O2 = CO2

So, I was also having trouble with my transient simulation, I wasn't getting any CO2 production and my temperature didn't change, but in the steady state condition, the reaction happened. With this first steady state result, I changed to transient and the reaction proceeded, although it didn't converge (10^-2 residuals at continuity). So it was one try that I made. Someone knows a more accurate approach?
souza.emer is offline   Reply With Quote

Old   December 20, 2018, 09:25
Default
  #10
New Member
 
Andrés Cimino
Join Date: Nov 2017
Location: Cordoba, Argentina
Posts: 2
Rep Power: 0
acimino is on a distinguished road
Quote:
Originally Posted by gr135 View Post
Okay, does it mean that I should start with steady analysis for few iterations and then continue with transient analysis? But would that simulation give me a video on how the flow the flame is developing in the flow?

My reasoning: I have given air inlet above 1000 degrees which is higher than auto-ignition temperature of methane so I expected flame without any igniter.

Thank you for the response.
The problem is in the equations used to model chemical reactions, i.e. the rate equations. Some depend also on the mass fractions of the products of combustion.
To start the flame I used a simple model that represents a pilot flame: a small inlet at a high temperature (say 2000 K) and with the mass fractions of the burned products of combustion of the fuel oxidizer mixture that you are trying to model.

I calculated those using NASA's CEA code:
https://cearun.grc.nasa.gov/index.html

Hope it helps
acimino is offline   Reply With Quote

Reply

Tags
combustion, fluent 17.2, transient

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Not able to setup the transient combustion modeling Sandip K FLUENT 0 November 21, 2013 01:26
Turbulent combustion error... XiFoam model achinta OpenFOAM 1 July 7, 2010 09:24
transient combustion and mesh adaption Peter CFX 4 April 20, 2006 19:23
combustion, chemical reaction or turbulent source? sogen Main CFD Forum 0 July 29, 2005 23:41
Methane turbulent combustion Julie Polyakh FLUENT 1 February 9, 2004 05:46


All times are GMT -4. The time now is 19:27.