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

iteration questions in discrete phase

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 13, 2014, 22:55
Default iteration questions in discrete phase
  #1
New Member
 
SinYoongWook
Join Date: Aug 2014
Posts: 5
Rep Power: 3
iknowjesus is on a distinguished road
hello, fellows.

I'm a beginner in fluent and try to do a coal gasification simulation..

I think i've set well other options and settings(maybe)

The divergence occur if i do directly start calculation. so i firstly simulated without coal injection and add coal injection, then the calculation was completed.

and i'm doing my job like that..

But, anyway, one of my reference paper says like this,

''For the finite rate model, where the Eulerian-Largrangian approach is used, the iterations are conducted by alternating between the continuous and the discrete phases. Initially, one iteration in the continuous phase is conducted followed by one iteration in the discrete phase to avoid having the flame die out. The iteration number in the continuous phase gradually increases as the flame becomes more stable. Once the flame is stably established, fifteen iterations are performed in the continuous phase followed by one iteration in the discrete phase. The drag, particle surface reaction, and mass transfer between the discrete and the continuous phases are calculated. Based on the discrete phase calculation results, the continuous phase is updated in the next iteration, and the process is repeated."

Water-gas shift modeling in coal gasification in an entrained-flow gasifier - Part 2: Gasifiaction application, X. Lu, T. Wang/ Fuel 108 (2013)


my question is this. So the authors are saying their computation was performed like this

15 (continuous phase iterations) - 1 (discrete phase iteration) - 15 (continuous phase iterations) - 1 (discrete phase iteration) - 15 - 1...

but is that possible in FLUENT? do they mean they did manually performed 15 iteration(continuous phase) and 1(discrete phase) and 15 and 1 bla bla..?

no matter how i try, i couldn't find automatically do like that in fluent


P.S. one more question..

if that kind of residual pattern(i attached image) occurs, can i trust the result?
i conducted over 6000 iterations.
Attached Images
File Type: jpg residual.jpg (65.7 KB, 20 views)
iknowjesus is offline   Reply With Quote

Old   August 14, 2014, 00:13
Default
  #2
Member
 
Sangwoo Kim
Join Date: Jul 2014
Location: Seoul, South Korea
Posts: 91
Rep Power: 3
swtbkim is on a distinguished road
I think the paper is saying about the number of continuous phase iteration per DPM iteration. I attached an image.
but i'm not sure.. somebody else will know well about it.


and residual graph itself looks cool if you are using transient solver.
but the solution should be validated in many perspectives as you know.

turbulence viscosity limitation is being warned, but the number of cells is decreasing. so I would keep calculating or control the residual criterion if I were you.
Attached Images
File Type: png 1.PNG (23.8 KB, 16 views)
__________________
Best regards
swtbkim is offline   Reply With Quote

Old   August 14, 2014, 03:47
Default
  #3
New Member
 
SinYoongWook
Join Date: Aug 2014
Posts: 5
Rep Power: 3
iknowjesus is on a distinguished road
Quote:
Originally Posted by swtbkim View Post
I think the paper is saying about the number of continuous phase iteration per DPM iteration. I attached an image.
but i'm not sure.. somebody else will know well about it.


and residual graph itself looks cool if you are using transient solver.
but the solution should be validated in many perspectives as you know.

turbulence viscosity limitation is being warned, but the number of cells is decreasing. so I would keep calculating or control the residual criterion if I were you.
Thx sang woo.

Ah.. however.. sadly.. this is steady-state simulation

then.. can I say that

1. the residual patterns means the calculation what i'm doing is soooooo unstable
2. so.. needs other solution, such as more iterations..?

but more iterations didn't make the residual patterns stable
as i mentioned above, i did more than 6000 iterations but still dizzy residual graphs were shown.

anyway i'll try as you have attached, lol

thank you soooooooo much.
iknowjesus is offline   Reply With Quote

Old   March 8, 2015, 19:56
Default DPM problem
  #4
apo
New Member
 
apostolis
Join Date: Oct 2014
Posts: 21
Rep Power: 2
apo is on a distinguished road
Hi all, iam working on a boiler problem and I am using group injection. My combusting material is coal mv, I am using combusting at material type and the devolatilizing species are mv_vol. The vaporization Temperature of the combusting material is 400K. When I use at injection initial Temperature T=400K, it's all ok, but when I use initial Temperature T=300K I have many problems, such as "Temperature limited to 1 or to 5000K. Is it wrong to have initial Temperature less than Vaporization Temperature?

Thanks in advance,
apo
apo is offline   Reply With Quote

Old   March 13, 2015, 07:07
Default
  #5
Senior Member
 
Paritosh Vasava
Join Date: Oct 2012
Location: Lappeenranta, Finland
Posts: 545
Rep Power: 12
vasava will become famous soon enough
Some time the limited temperature may vanish as your simulation progresses. But if it does not then you must take a close look at your mesh and simulation setup.

There are number of reasons why you have the limited temperature warning. I think first you must check your mesh (not just quality but fineness also) and make sure you have good mesh. Then you can check the solution methods and make sure that you use higher order discretization schemes. Also use lower relaxation factors.

Also you can go to solution controls and then click limits. Here you can have upper and lower limits for temperature.

Further you can check the problem area with Iso-value adaption.
vasava is offline   Reply With Quote

Reply

Tags
discrete phase, dpm, fluent, gasification, iteration

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
report discrete phase data problem. seasoul FLUENT 0 April 22, 2008 01:10
discrete phase example aliiii FLUENT 0 December 5, 2007 16:49
weired behavior in discrete phase Arash Kashani FLUENT 2 August 30, 2006 16:12
questions with Discrete Phase cwflying FLUENT 5 July 18, 2002 07:07
Discrete Phase Modeling X.Tang FLUENT 0 April 25, 2000 08:17


All times are GMT -4. The time now is 14:35.