CFD Online Logo CFD Online URL
Home > Forums > FLUENT

Continuity convergence problem

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

LinkBack Thread Tools Display Modes
Old   December 13, 2010, 16:54
Default Continuity convergence problem
New Member
Ankur gupta
Join Date: Aug 2010
Posts: 5
Rep Power: 9
ankur gupta is on a distinguished road

I am using a 2-phase, euler model to model laminar mixing flow across static mixers.
I am using a uniform tet mesh. Using 3-D,double precision

My continuity does not seem to converge. Residual is around 1.0e-03.

I have tried -:
1) increasing mesh density
2) increasing downstream length
3) changing the under-relaxation factor, it helps only a little.

When I use two similar fluids (of same viscosity) the convergence is still better, around 2.0e-05. But when the fluids are of extremely different viscosity (ratio 1:1000), the convergence is 1.0e-03

Can somebody please help me. I really need help with this

ankur gupta is offline   Reply With Quote

Old   December 13, 2010, 19:36
Senior Member
Real Name :)
Join Date: Jan 2010
Location: United States
Posts: 192
Rep Power: 9
ComputerGuy is on a distinguished road
2e-5 seems reasonable, although often the best way to determine convergence is to look at the flow variables (mass flow, for instance) and see the total imbalance in the system.

If the mass in is approximately equal to the mass out, the pressures are behaving as you expect, etc., you might consider the solution converged, whether or not it reaches some arbitrarily low value for residuals.

Also, how are you refining the mesh? If you're refining in Fluent and you have a number of highly skewed cells, Fluent won't really decrease the skewness. It's better to return to design modeler or gambit and simply improve the mesh that way.
ComputerGuy is offline   Reply With Quote

Old   December 13, 2010, 20:23
New Member
Ankur gupta
Join Date: Aug 2010
Posts: 5
Rep Power: 9
ankur gupta is on a distinguished road

thanks for your reply..

2.0e-5 is coming when the viscosities of the fluids are same..

and 1.0e-3 is coming when the viscosities are very different..(1000 times)

i am refining skewness from fluent..

but do you think creating a dense mesh near the high gradient region will help ??
ankur gupta is offline   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
Convergence of Continuity Dodi FLUENT 0 February 28, 2009 17:03
Convergence Problem AAJ FLUENT 2 July 3, 2008 13:31
Convergence problem for P1 & Energy HP FLUENT 5 May 21, 2005 15:01
Non Convergence of 3D Heat transfer cfd problem Balraj Main CFD Forum 3 December 9, 2004 01:24
High Continuity Residual for 3D problem Gearoid Lydon FLUENT 5 July 27, 2000 08:09

All times are GMT -4. The time now is 18:27.