Fluent Batch Mode wont converge
 

Hi All,

I am trying to run fluent in batch mode. I used the command below

/solve/dual-time-iterate 24000 50

I found an explanation that 24000 is the number of time steps and 50 is the max number of iterations per time step. I have also set tolerance to be 1e-6 under Monitors>Residuals.

However, during the batch process, i have also tried changing the "50" to different values like 100, or 150. I realised that Fluent will conduct the exact number of iterations that I specify.

On the contrary, I have tried running the same case and dat file offline with my own computer. The number of iterations will stop at about 30, once the tolderance of 1e-6 is reached, and the iteration is terminated and the next time step starts.

What am I doing wrong and why is that when I run Fluent in Batch mode, my results won't converge and calculations are made all the way till my specified value?

Thanks!

here are two screenshots, one in batch and the other is offline iteration.

What I meant was the exclamation mark that marks the convergence of each time step.

*I don't think you can change anything once the batch has started

*On your 2 screenshots, you aren't comparing exactly the same thing.
With the batch you are showing Time step 424 which didn't converged after your 50 iterations.
Within fluent you are showing the first time step which converged before your max iterations.

If the first timestep will converge in 30 iterations (for example) it doesn't mean that every time step will also converge within 30 iterations

Oh my apologies, perhaps I didnt state myself clearly. The screenshot that I label "solved" by my computer is just an illustration to show the "exclamation mark".

I did not manage to capture an image of my computer's screen at time step "23575", the same time step as the batch solver. But I am fully certain that my solutions converge between 18-28 iterations at tolerance 1e-6 when I solve with my PC.

In fact, for batch mode, my solutions do not converge. and if u look closely at the image i have uploaded, some iterations cause an increase in residues. It just calculates all the way till 100 and it doesn't really care about residues.

check at least for the first time step if both are converging

Hi Max,

I really thank you for your fast reply!

When running on my computer, the iterations converge at about 26-28, I couldn't really remember the exact number. But I am fully sure that it is below 30.

As for the batch mode solver the iterations do not converge at all. The iterations will just keep running till it hits my specified number.

copy and paste your project somewhere, and just try to re-run only for the first time step in batch mode and also in GUI
Are they both converging?

Hi Max,

I have attached 2 images, one is by batch the other is by computer. You may see that the batch solver has even reached over 400 iterations and still yet to converge... :'( The PC-solved image shows convergence at 60iterations...

no, with your batch I still see time step 424.
I wanted to see time step 1 (just like with GUI)
If both are converging, then the residuals monitoring/check is ok
Attachment 42832

Oh I get it!

I have attached the image below... Thanks!

Alright,
now it is clear that your continuity isn't converging with batch.
If I compare both methods, I can see the flow-time after first time step, which means I get your dt.
If you compare them, you have dt=1e-4s for GUI and 5e-4s for batch.
So you cannot compare both methods since the one with smaller dt will converge faster than the other
Now set both dt with 1e-4s and compare again
Attachment 42834

I have changed the time step and i have attached the image for GUI. It converged before reaching 70..

Set the case for batch with dt=1e-4s and re-run