CFD Online Logo CFD Online URL
Home > Forums > CFX

Convergence issue

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

LinkBack Thread Tools Display Modes
Old   March 4, 2007, 15:07
Default Convergence issue
Posts: n/a
I have a model of a straight pipe, I am using to get a fully developed profile to use in my pipe junction.

I am using an SST model. Funnily, I seem to have no convergence even after about plenty of iterations. The behaviour is bouncy but it does not even try to go down even a tiny bit.

I tried playing with the timestep. But that didn't work.

But funnily enough, when I refine the mesh, I get convergence as low as E-12 in just 5 iterations. So what can my problem be?

I use CFX mesh to create the mesh. While trying to keep the Y+ less than 1.

Thanking in anticipation

  Reply With Quote

Old   March 4, 2007, 18:41
Default Re: Convergence issue
Posts: n/a
Something is really very wrong when you get convergence to 1e-12 in 5 iterations. This cannot be a converged solution!

When you use SST and find a lot of flow separation at delicate locations you won't ever get convergence. Have you exported residual values to your res-file? What do these tell you?

Have you tried k-e with scalable wall functions? This should converge quite fast as it clips to y+=11.

What do you define on the in- and outlet in terms of turbulence?

  Reply With Quote

Old   March 7, 2007, 11:37
Default Re: Convergence issue
Posts: n/a
Well, my inlet velocity is 210 m/s. I did a little calculation for my branch of diameter- 16 inches. And found out that the trubulence intensity would be around 2.3%.

My outlet is a pressure out, at 0 atm. I will try to see how K-epsilon does.

Have I exported residual values to your res-file? I am not really sure what that is, and how it may help? Would you please help me understand?

Thanx for replying Astrid!
  Reply With Quote


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
Force can not converge colopolo CFX 13 October 4, 2011 22:03
Convergence of CFX field in FSI analysis nasdak CFX 2 June 29, 2009 01:17
Convergence issue in SST for Porous model Raj CFX 0 May 2, 2008 02:43
CFX-Solver, issue with convergence behavior Andy CFX 7 September 5, 2006 03:24
Convergence issue with continuity equation Jake FLUENT 6 June 15, 2005 16:14

All times are GMT -4. The time now is 22:02.