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

Implicit steger warming fvs

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

Reply
 
LinkBack Thread Tools Display Modes
Old   May 18, 2011, 17:05
Default Implicit steger warming fvs
  #1
New Member
 
dushyant
Join Date: May 2011
Posts: 6
Rep Power: 6
pooja is on a distinguished road
Hiiii, i am writing code for the implicit steger warming flux vector splitting for 1d cd nozzle case. i am using gmres method to solve Ax = b.
One strange thing is happening with in the code, as all of us know that for implicit there is no restriction on CFL number, First point is that if i start with CFL value 0.1 and max CFL value 2, with incrementation in CFL given by CFL*1.1 my code is converging nicely upto log rss value -7.034528 and results are matching.
But if i am taking max CFL number more than 2 say 4 the its blow up and go for log rss value -1.234 so on or if further increase in max CFL say upto 10 i will get nan after some iteration. I am really getting fed up with it from last one month then one of my friend told that u can put your problem in cfd forum surely you will get nice ideas. All ideas are welcome and thanks in advance plz help me
pooja is offline   Reply With Quote

Old   May 19, 2011, 00:10
Default
  #2
Super Moderator
 
praveen's Avatar
 
Praveen. C
Join Date: Mar 2009
Location: Bangalore
Posts: 248
Blog Entries: 6
Rep Power: 9
praveen is on a distinguished road
gmres is not easy to get working for flows with shocks.

From your description I assume you are solving a steady state problem.

You do need to use a smaller cfl to begin with. You can slowly increase this as your residual decreases. So you can try something like

cfl^n = cfl^{n-1} \frac{Res^{n-1}}{Res^n}

You can also put an upper bound on the cfl.

Note that without good preconditioner, gmres will not work.
praveen is offline   Reply With Quote

Old   May 19, 2011, 05:34
Default
  #3
New Member
 
dushyant
Join Date: May 2011
Posts: 6
Rep Power: 6
pooja is on a distinguished road
Thanx parveen for reply, but for 1d cd nozzle case as i said earlier i am starting with a low value of CFl 0.1 and incrementing with CFL*1.01 .
Shall i have to change the iterative method ?
pooja is offline   Reply With Quote

Old   May 19, 2011, 06:48
Default
  #4
New Member
 
dushyant
Join Date: May 2011
Posts: 6
Rep Power: 6
pooja is on a distinguished road
Hey only, one reply from this forum not expected I am really in very much trouble help me plzzzzzzzzzzz
pooja 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
Help. implicit discritization dearboy Main CFD Forum 0 November 25, 2010 22:46
Can anyone explain the difference between these implicit concepts? bearcat Main CFD Forum 0 February 20, 2010 19:39
Help regarding Steger Warming Scheme Sunny Main CFD Forum 2 July 27, 2006 15:53
how implicit is implicit? Joe cool Main CFD Forum 7 July 16, 2004 11:10
UDF : Chemical Reaction in Catalytic Converter adhimac FLUENT 1 March 27, 2001 14:04


All times are GMT -4. The time now is 14:25.