Combustion stops after a few 100 iterations..

the_sixth_hokage · May 1, 2020, 02:16

Hi...

I'm modelling EDC , species transport combustion of cryogenic fuels (CH4/LOX) under trans critical conditions..

I montior the temperature contours (using animation) and found that flames are produced...the flame shape changes after every 10 itreation...

The residuals are good and when it is nearly converged there is no combustion occuring, only mixing of fuels..

Even when I patch a high temperature the flame shape appears for some iterations but it goes away...I have tried to patch multiple times...but each time the flame disappears...

Does anyone know why this is happening??!

vinerm · May 1, 2020, 15:44

Are you using ISAT or some other mechanism to increase the speed? If yes, then patching with high temperature is not a good idea. Rather, try to purge the table and let it rebuild.

the_sixth_hokage · May 1, 2020, 21:58

Quote:

Originally Posted by vinerm

Are you using ISAT or some other mechanism to increase the speed? If yes, then patching with high temperature is not a good idea. Rather, try to purge the table and let it rebuild.

Yeah I'm using isat...so I should clear the table and then patch??!

Krutika Appaswamy · May 2, 2020, 11:57

I am having the same issue with combustion but while using PDF transport method.. Any idea why this is happening? Thank You!

vinerm · May 2, 2020, 16:33

Clear the table but do not patch. Patching is not always helpful. In case you do not see any combustion, then patch.

the_sixth_hokage · May 4, 2020, 04:09

Quote:

Originally Posted by vinerm

Clear the table but do not patch. Patching is not always helpful. In case you do not see any combustion, then patch.

I tried clearing the isat table and ran the simulation...but it was of no help..

So I patched with high temperature (2500K)...I observed flames for a few 50 iteartion...then it began diassapering again and became like the original flameless contours...

MKuhn · May 4, 2020, 09:11

I have no experience with modeling of combustion. But it seems that the flame depends on a certain temperature level. With patching you hook the temperature of your domain to that level, only for the starting point of your simulation.
Check your boudary conditions, try to increase the temperature of your inlet streams and/or of your walls, to avoid a cool down of your domain.

vinerm · May 5, 2020, 08:33

Then the issue is most likely with the generated table or with turbulence interaction. It is possible that fine-scale time is too small. You can try with reduced acceleration factor, make it close to 0.

Krutika Appaswamy · October 7, 2020, 12:14

Hi,
I have been having the same issue with combustion and I remember reading that reducing the integration parameters initially helps in ignition. I remember something like this worked for me then but I am unable to get it to work now. I was wondering if that is true and if so, how to start the case to ensure sustained combustion.
Thank you!

May 1, 2020, 02:16	Combustion stops after a few 100 iterations..	#1
the_sixth_hokage New Member Lee Jo Join Date: Mar 2020 Posts: 29 Rep Power: 6	Hi... I'm modelling EDC , species transport combustion of cryogenic fuels (CH4/LOX) under trans critical conditions.. I montior the temperature contours (using animation) and found that flames are produced...the flame shape changes after every 10 itreation... The residuals are good and when it is nearly converged there is no combustion occuring, only mixing of fuels.. Even when I patch a high temperature the flame shape appears for some iterations but it goes away...I have tried to patch multiple times...but each time the flame disappears... Does anyone know why this is happening??!

May 1, 2020, 15:44	Isat	#2
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	Are you using ISAT or some other mechanism to increase the speed? If yes, then patching with high temperature is not a good idea. Rather, try to purge the table and let it rebuild. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

May 2, 2020, 11:57	Same issue with combustion	#4
Krutika Appaswamy New Member Krutika Appaswamy Join Date: May 2020 Posts: 8 Rep Power: 6	I am having the same issue with combustion but while using PDF transport method.. Any idea why this is happening? Thank You!

May 2, 2020, 16:33	Isat	#5
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	Clear the table but do not patch. Patching is not always helpful. In case you do not see any combustion, then patch. the_sixth_hokage likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

May 5, 2020, 08:33	Table	#8
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	Then the issue is most likely with the generated table or with turbulence interaction. It is possible that fine-scale time is too small. You can try with reduced acceleration factor, make it close to 0. the_sixth_hokage likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

May 4, 2020, 09:11		#7
MKuhn Senior Member Moritz Kuhn Join Date: Apr 2010 Location: Germany, Dresden Posts: 207 Rep Power: 17	I have no experience with modeling of combustion. But it seems that the flame depends on a certain temperature level. With patching you hook the temperature of your domain to that level, only for the starting point of your simulation. Check your boudary conditions, try to increase the temperature of your inlet streams and/or of your walls, to avoid a cool down of your domain.

October 7, 2020, 12:14	Same issue with combustion	#9
Krutika Appaswamy New Member Krutika Appaswamy Join Date: May 2020 Posts: 8 Rep Power: 6	Hi, I have been having the same issue with combustion and I remember reading that reducing the integration parameters initially helps in ignition. I remember something like this worked for me then but I am unable to get it to work now. I was wondering if that is true and if so, how to start the case to ensure sustained combustion. Thank you!

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