I know in Ansys CFX, you can use the option "Opening" at the outlet for the reversed flow. You can check, how to implement the same in Fluent. Also, you can check the link below. You may find it useful.

https://forum.ansys.com/discussion/6481/fluent-setting-an-open-boundary

Thank you, dear Kumar. I'll watch the video and search more about 'opening'.

Hi Lara Emilly Pereira Santos ,

Would you please explain this boundary condition a little bit more? Are the mass flow rates known in these two processes? If yes, in ANSYS Fluent, you can change the boundary condition from velocity/mass flow inlet to mass flow outlet (or velocity inlet with a negative value).

Hi Ashkan Ghafari,

Yes, the mass flow is known as well as pressure variation during the process. You told that I can set the inlet as outlet after (if I understood well) but I would have to do this after the first simulation (inspiration), right?

I would like that this change was done automatically. This is the problem: the same face that works as inlet in inspiration will work as outlet in expiration, and these processes happen one after the other.

Do you know some way that I could do this?

Lara Emilly Pereira Santos as I understand, the problem is that, for example, in the first 100 time steps, the boundary condition should be mass flow inlet, and in the next 100 steps, it should be changed to pressure outlet or mass flow outlet.

This can be done automatically by defining execute command in fluent.

Yes, Ashkan Ghafari ! Is exactly this!

Can you explain to me how can I do this? Or recommend some papers that will help me?

Thank you for your help.

Hi Lara Emilly Pereira Santos ,

I'll send you a video tomorrow. You can also read its settings in Fluent User's Guide.

Sorry for the delay, this is the video. Lara Emilly Pereira Santos

Thank you very much, Ashkan Ghafari !

I will watch the video. If remain some doubt can I ask you again?

Thank you in advance!