Restarting cold flow simulation introducing combustion model

[fracenvi]

Hello,

I'm trying to collect statistics for a simulation case which runs for a very large number of cells and the combustion module on.

Henceforth, what i'm doing is running the case first deactivating the combustion to have a first set of statistics (cold flow case) because it will eventually converge faster and then i restart the simulation activating the module (this is the same procedure i was using with other codes, and it was working fine). However, i noticed that the simulation crashes after the first iteration because of this error:

Runaway computation:
At least one field exceeded allowed bounds (see log).

Is this procedure even possible using code_saturne? In case yes, any ideas on how to sort this out?

Thanks a lot for the help and regards,
Francesco

[Yvan Fournier]

Hello,

Restarting with a change in model should work in theory, but a strong variation in computed values can lead to divergence in some cases.

First, did you check that the combustion case does not diverge if you run it for a few time steps directly (i.e. not as a restart) ? If this is OK, you should check in the log which initial field values may be different in the computation and in the restart (for axempla maybe the mixture fraction), and if any, force the matching values after the restart in the cs_user_initialization function.

Also, v7.0 is not maintained anymore, so switching to v9.0 may be better (though I do think of any change specific to this matter). Also, you have many warnings about the time step. Did you force a 2nd order time scheme ?

Best regards,

Yvan