|
[Sponsors] |
November 26, 2012, 03:27 |
residuals still going down!
|
#1 |
Senior Member
christine
Join Date: Jul 2009
Location: europe
Posts: 125
Rep Power: 16 |
Hello,
I'm running a case of turbogas. When I work on the "cold" case, to test the mesh, the residuals are never "plane". What could be the problem? same problem when switching on combustion. I send you the pictures of these residuals. http://cjoint.com/data/0KAjAQL9Y2T.htm on which parameters should I "play" ? thank you very much for any help yorelchr |
|
November 26, 2012, 04:36 |
|
#2 |
Senior Member
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,297
Rep Power: 26 |
Residuals look quite normal to me. What exactly do you think the problem is? That some residuals start jittering at 1.0e-11 or that some of the others (continuity) are not "plain"?
How many cells does your grid have? 20,000 iterations seem to be pretty much... Maybe you can get faster convergence with a different solution method. |
|
November 26, 2012, 08:42 |
|
#3 | |
Senior Member
Rick
Join Date: Oct 2010
Posts: 1,016
Rep Power: 26 |
Quote:
To see if you have a converged solution monitor some parameters (species concentration, velocity, pressure, other..) on some planes into your domain; if they don't change with successive iterations, you have a converged solution. |
||
November 28, 2012, 16:13 |
residuals and combustion
|
#4 |
Senior Member
christine
Join Date: Jul 2009
Location: europe
Posts: 125
Rep Power: 16 |
thank you Rodriguez Fatz and Ghost 82 for your help and sorry to reply so late.
I thought residuals should be plane, but I monitored some variables and it seems ok. I have another question : my geometry is extracted from a bigger one. Since the bigger one has too many cells I have cut the domain and I put profiles coming from the entire turbogas simulations and I've kept the same mesh (it has been possible since the entire geometry has been meshed by block and I kept the original blocks (except of course the ones that I have eliminated). So, the strange thing is that the first 3000 iterations, my residuals are going down, really low...then the monitoring of the variables tell me that everything is changing and after many new iterations, I obtain the same results as with the entire domain. But with the entire domain, there is no need to wait for these first 3000 iterations, the "final results" are coming quicker....so if had not the full domain, I would have stopped my simulations during the first 3000 iterations since nothing anymore was happening...so...why this difference between the full domain and the extracted one? (at this stage, there is no combustion, it's just for testing the mesh and checking the velocity profiles) Thanks for any clue... yorelchr |
|
November 29, 2012, 07:09 |
|
#5 |
Senior Member
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,297
Rep Power: 26 |
Maybe:
The equations of the reduced case differ from the complete case. Not only the full case has a larger system of equations, but also the boundary conditions are different, i.e. the bc of your reduced case lie somewhere inside your complete domain. So in one case the bc are "hard wired" to some value, whereas in the other (complete) case the same cells have to be calculated. Also the solver will behave differently with two different sets of equations. Then, the initialization differs and so on... I would not be too suprised by this behavior.
__________________
The skeleton ran out of shampoo in the shower. |
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
[Tutorials] Tutorial of how to plot residuals ! | wolle1982 | OpenFOAM Community Contributions | 171 | February 20, 2024 02:55 |
under-relaxation factors -> level of residuals | Zigainer | FLUENT | 19 | July 21, 2017 16:53 |
what to monitor besides residuals? | franzdrs | FLUENT | 5 | March 21, 2013 03:59 |
Strange residuals of the Density Based Solver | Pat84 | FLUENT | 0 | October 22, 2012 15:59 |
Convergence - scaled vs unscaled residuals | HS | FLUENT | 1 | November 7, 2005 05:45 |