[juan4815]

Hello,
I've been working with CFX on the ventilation of engine emissions in a maintenance workshop and I encountered a problem regarding the residuals during the simulation.

During the steady state solution (for the initial conditions of the transient one) everything is fine, but when working the transient sim the residuals (momentum, turbulence variables, imbalances) oscillate highly with periods of 0.05 sec to 0.1 sec approximately.

The solution in large timescales, over 30 seconds, it's fine and doesn't have any abnormalities, so apparently it's not a problem of convergence of the solution (topic that is covered in related threads, which I reviewed). I tried changing some parameters like min time step, incresing time step factor, max time step, without any appreciable effect.

I think it may have something to do with the numerical scheme being used, but I'm not entirely sure how to approach this problem as I'm fairly new to CFX (and to this forum too, I hope this is enough information as a starting point to a discussion, I didn't know what other info to give at this point).

I appreciate any information o suggestion you could give to understand and eventually fix this issue.
Regards