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

reversed flow and divergence

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

Like Tree1Likes
  • 1 Post By callofduty

Reply
 
LinkBack Thread Tools Display Modes
Old   April 7, 2009, 15:24
Default reversed flow and divergence
  #1
New Member
 
Howard
Join Date: Mar 2009
Posts: 5
Rep Power: 7
mechfloeng is on a distinguished road
Hi, I have following message:

reversed flow in 80 faces on pressure-outlet 4.
Error: divergence detected in AMG solver: x-momentum
Error Object: ()

Can I get help, how can I solve it?

Thanks
HW
mechfloeng is offline   Reply With Quote

Old   April 8, 2009, 05:05
Default
  #2
New Member
 
Tenar
Join Date: Apr 2009
Posts: 3
Rep Power: 7
callofduty is on a distinguished road
Hi Howard,
first of all i recommend you to increase your maximum limits as much as possible(solve>controls>limits) (i think your face number-which reversed flow problem occurs- is controllable.)
Moreover you can start fmg initilization by solve>initialize>fmg initilization. FMG initilization provides better convergence.
If problem continues i recommend you to check your grid if your skewness is high.
But i hope you dont need it

Ciaooo
Tenar
alimoh1987 likes this.
callofduty is offline   Reply With Quote

Old   April 8, 2009, 11:12
Default
  #3
New Member
 
Howard
Join Date: Mar 2009
Posts: 5
Rep Power: 7
mechfloeng is on a distinguished road
Hi, Tenar,

maximum limits of 1e+20 is allowable.
I cannot find menu FMG initilization in solve>initialize>fmg initilization. Can you tell me
how to get this menu? My skewness is high, how can I fix it?

Thanks
HW

PS here is my grid check
-------------------
Grid Check
Domain Extents:
x-coordinate: min (m) = 9.288283e-015, max (m) = 3.139997e+000
y-coordinate: min (m) = 8.000000e+000, max (m) = 1.000000e+001
z-coordinate: min (m) = -1.570000e+000, max (m) = 1.570000e+000
Volume statistics:
minimum volume (m3): 6.394585e-008
maximum volume (m3): 1.183709e-002
total volume (m3): 9.413165e+000
Face area statistics:
minimum face area (m2): 1.300699e-004
maximum face area (m2): 1.211852e-001
...............
---------------------
mechfloeng is offline   Reply With Quote

Old   April 8, 2009, 14:22
Default
  #4
New Member
 
Tenar
Join Date: Apr 2009
Posts: 3
Rep Power: 7
callofduty is on a distinguished road
You wont use fmg from menu.On fluent when you pres enter you will see some directories as

adapt/ file/ report/
.... .... solve>

you will write "solve" and press enter , so you'll be on 'solve' directory..
when you press again again sub-directories will be seen. You will choose 'initialize' and under sub-directory of 'initialize', there is function 'fmg initialization'. When you write the name of function, fluent will ask if you want to run 'fmg initialization'. So you can run it. For further detail you can look on FLUENT manual.

About your grid, i dont have any idea because your note does not contain any info. about grid skewness. If I were you, first i would check if my grid properly fit on geometry(if your model is complex), then i would be careful about my surface skewness is less then 0.8.

Let me know about your work, these are the basic solutions. There may be a problem about your boundary conditions or solution technique also!

Tenar
callofduty is offline   Reply With Quote

Old   April 9, 2009, 01:31
Default
  #5
New Member
 
Howard
Join Date: Mar 2009
Posts: 5
Rep Power: 7
mechfloeng is on a distinguished road
Hi, Tenar,

My case is for mixture (two phase), unsteady,
So computer show me:
---------------------------
/solve/initialize> fmg-initialization
FMG initialization is not available with the unsteady solver.
-------------------------------
If you like, please send your email address to me: mechflo@gmail.com
so I can send email to you.

Thanks
HW
mechfloeng is offline   Reply With Quote

Old   April 25, 2009, 23:46
Default
  #6
New Member
 
irineupetri
Join Date: Mar 2009
Posts: 7
Rep Power: 7
irineupetri is on a distinguished road
The message "reversed flow" can to cause a problem on the convergence, for take off this message, you should put in the comand line [solve/set/flow-warnings?/no] + enter

or

[solve] + enter
[set] + enter
[flow-warnings?] + enter
[no] + enter
irineupetri is offline   Reply With Quote

Old   August 10, 2010, 00:24
Default
  #7
Senior Member
 
Mohsin Mukhtar
Join Date: Mar 2010
Location: South Korea
Posts: 249
Rep Power: 7
Mohsin is on a distinguished road
Hello

I have following querries regarding FMG initialization. I will be grateful for your kind look at these:

1. When I run Fmg initialization without starting any iterations then it gives me the following error:

/solve/initialize> fmg-initialization
invalid command [fmg-initialization]

Please specify. Why it is so. As its prime function is to give the initial solution so isn't it should be specified before iterations?

2. When FMG initialization is complete I get the following message:

FMG: Initialize flow for Segregated solution.. . end

It means that FMG initialization has been done and after this I dont need to change the initial values from solve...> initialize. And I only have to iterate now?

3. I am using multiphase flow DPM. But first i think i should run FMG initialization without DPM and then introduce DPM later(making it single phase in order to for FMG initialization to run). Is it possible.

Please help me. I will be grateful

Mohsin
Mohsin is offline   Reply With Quote

Reply

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
Nozzle Flow - Divergence Problem Ijaz FLUENT 9 January 11, 2014 04:36
multiphase flow, quick divergence of contuinity eq violet FLUENT 7 February 3, 2009 17:54
flow past a missle: how to solve divergence? xiaofish FLUENT 0 September 9, 2007 22:53
Divergence of Laminar Flow With Eddy ??? Peter Kostka Main CFD Forum 3 May 9, 2002 17:02
about combustion in fluent Mark FLUENT 1 May 10, 2001 14:36


All times are GMT -4. The time now is 23:58.