|
[Sponsors] |
March 9, 2016, 02:15 |
Ensure convergence at eachtime step
|
#1 |
New Member
Amit Ray
Join Date: May 2014
Location: Chennai, India
Posts: 5
Rep Power: 12 |
Friends I am new to Fluent and I am doing a transient simulation in Fluent. I just need a small help. I want to know how we can ensure that at each time step the simulation converges. I mean as manually I can check that at certain time step the solution converged but suppose there are 2000 time steps and it is not possible to check convergence at each time step manually, so is there any method which can give me the data that at certain time step the solution didn't converge.
|
|
March 9, 2016, 04:49 |
|
#2 |
Senior Member
Cees Haringa
Join Date: May 2013
Location: Delft
Posts: 607
Rep Power: 0 |
Hi Amit,
You can set convergence criteria (on velocity, temperature, ..., and the residuals of course). If these criteria are met, the simulation will jump to the next timestep. So, set the criteria such that you are sure the relevant parameters are sufficiently converged inside a timestep, and choose the number of iterations per timestep such that the convergence criteria are virtually always met before the number of iterations criterion is fullfilled. That should ensure you are safe. |
|
March 9, 2016, 05:48 |
|
#3 | |
New Member
Amit Ray
Join Date: May 2014
Location: Chennai, India
Posts: 5
Rep Power: 12 |
Quote:
|
||
March 9, 2016, 06:03 |
|
#4 |
Senior Member
Cees Haringa
Join Date: May 2013
Location: Delft
Posts: 607
Rep Power: 0 |
Hi Amit,
In any case I would reduce your timestep size a bit. Although i don't have the reference at hand, I do recall reading somewhere that transient simulations should target at converging in 20-50 iterations per step to ensure all features are captured (if someone disagrees or has the reference, please throw it in!) On what basis do you conclude convergence by the way? I often set the targets quite strict, so that even when the criteria are not met, the situation is likely acceptable. Of course it should be possible to write a UDF; the macro N_ITER gives the iteration number so if you export that at the end of each timestep, you know the number of iterations per timestep. But, you can also simply export a monitor each iteration rather than each timestep (for example, average velocity). You can easily see if that converges per timestep then, in excel, matlab, etc. |
|
March 10, 2016, 02:09 |
|
#5 | |
New Member
Amit Ray
Join Date: May 2014
Location: Chennai, India
Posts: 5
Rep Power: 12 |
Quote:
|
||
March 11, 2016, 06:46 |
|
#6 |
New Member
ami
Join Date: Dec 2015
Posts: 8
Rep Power: 10 |
Hello,
To have convergence between each time step, you have to switch off convergence criteria in the monitors section as shown in the picture. |
|
Tags |
convergance, fluent, time steps |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Ensure UDF runs only once a time step | PranjalNewton | Fluent UDF and Scheme Programming | 1 | October 18, 2015 07:06 |
PimpleFoam: check for convergence within time step | Begineer | OpenFOAM Running, Solving & CFD | 3 | April 21, 2014 18:42 |
Time step size & convergence absolute criteria | yuitsang | FLUENT | 5 | April 15, 2013 05:27 |
same geometry,structured and unstructured mesh,different behaviour. | sharonyue | OpenFOAM Running, Solving & CFD | 13 | January 2, 2013 23:40 |
Force can not converge | colopolo | CFX | 13 | October 4, 2011 23:03 |