[dgnidovec]

Hello,

I am encountering a warning message in Fluent when loading a steady-state solution as an initialization for a transient analysis. The warning message states: "Warning: The time step size (0.1) in the session did not match the time step size in the data file (1), and has been overwritten by the value from the data file."

From my understanding, the steady-state solution does not have an explicit time step size, as it is a time-independent analysis. However, Fluent requires a time step size for transient simulations. Therefore, when I load the steady-state solution, Fluent automatically assigns a default time step size of 1 to match the time step size in the data file.

This warning message occurs consistently, and I would like to understand if there is a way to resolve or suppress it. The reason I would like to resolve this problem is that I have defined 3 UDF's for my transient analysis where I am using N_TIME macro and it affects the current time step number, because the first iteration has this number 0 instead of 1 as all the further ones. Anyway I can run the simulation with the time step 0.1s, because I overwrite it in my journal file. But as I mentioned it affects the N_TIME macro that is necessary for my multi-scale modeling.

I have explored various options within Fluent, such as adjusting the time step size in the session settings (pseudo-time step...), but it seems that the default value from the data file always takes precedence.

Has anyone else encountered this warning message when loading a steady-state solution for initialization in a transient analysis? If so, I would appreciate any insights or suggestions on how to handle this situation.

Thank you in advance for your assistance.

Best regards,
Domen

[MKuhn]

Hello Domen,


you can change the flow time in the dat-file via TUI
To start with time zero:


In the TUI type with brackets, both values should be reset:
(rpsetvar 'flow-time 0)
(rpsetvar 'time-step 0)


To query the values:
(rpgetvar 'flow-time)
(rpgetvar 'time-step)


Moritz

[dgnidovec]

Originally Posted by MKuhn

Hello Domen,


you can change the flow time in the dat-file via TUI
To start with time zero:


In the TUI type with brackets, both values should be reset:
(rpsetvar 'flow-time 0)
(rpsetvar 'time-step 0)


To query the values:
(rpgetvar 'flow-time)
(rpgetvar 'time-step)

Moritz

Thank you very much for your reply. It does indeed change the number of time step and the flow time analysis, but there is one more problem. Because fluent somehow does not match the time-step-size it does one iteration with time step size 1.0s (as set from steady-state analysis) and then changes to the time step I set (0.1s). I append the image of the output where the latter happens. If I set the number of time step to 0 it starts with 0 and proceeds to 1, if I set the time step number to 1 it starts 1 and proceeds with 2, but in any case it changes the number of time step. I need this value of N_TIME macro constant over the whole time-step and it should be 1 for the first time step, 2 for the second time step and so on...

I hope my problem is clarified enough.

Best regards,

Domen

[MKuhn]

May this helps:
run your steady state solution, in transient mode with only one time step and with BC setting where nothing will happend and save the data file.

[dgnidovec]

Originally Posted by MKuhn

May this helps:
run your steady state solution, in transient mode with only one time step and with BC setting where nothing will happend and save the data file.

I am dealing with the multi-scale modeling. That means I am exchanging data between 0D model and 2D/3D model in fluent. First step is to run steady-state analysis in fluent and then start the simulation in the following way:
- initialize first time step with steady-state data and run transient analysis for 1
time step
- send transient data to 0D model and then calculate the results
- send this results back to fluent model and iterate till the values at the end of
time step converge


When values at the end of time step converge, I move to the next time step. So basically my journal file is fine for all the time step (also N_TIME macro), I just encounter the problem when running the first time step when initializing with steady-state data. When I initialize fluent simulation with transient data, it works fine. Any suggestions or experiences with that?

Best regards,

Domen

[MKuhn]

No sorry I have no detailled experiences in that, so unfortunatly no more hints from my side.