outflow its OK!

OK, I have tried a lot the outflow, but i always get reversed flow and also the problem of convergence. how did you solve your problem?

I decreased at least the different under-relaxation factor (0.1 and 0.2) because in the beginning of simulation we have very significant disruption to overcome so you should lower these values, then when the solution begins to stabilize you can increase it gradually

OK, I will have a try. Thank you.

Steven,
Is your problem fixed?
Don't focus on reversed flow warning.
The convergence is the one you need to fix.
Maybe you should consider & switch on unsteady solver, if rayan's tipp didn't help you.
Did you also try to compute on a much finer grid?

Thank you Max.

I have solved the problem of convergence. Do you remember the gambit file that i sent to you. I united the two volumes in the center, then it worked without warning under the model 'outflow'. This makes me confused, I don't know why this works. Do you know what happened?

Good to read you solved your problem.
But sounds weird.
Anyway it is solved (maybe an internal surface or whatever, but I checked and everything was ok)

You are right, it is a problem of interface. I came to know why just now. My professor told me that i overlapped two faces together at the entrance of the small tube. When i united them together, i removed the face which caused problem.

Anyway, Thank you so much.

yes, typical error in Gambit :D

Hello Max,
I have a question, how can i creat a face to mesure the pressure of my larger tube depending on the lenghth?
Thank you.
Steven

you can do that in fluent, post-processor.
I cannot remember the exact name, I can tell you on Monday when I return at the office.
Kids are giving more troubles than mesh.... :)

Hi, I'd go to Insert/Location/Plane in CFD-Post. Then define the plane (e.g., z=constant) and plot the desired variable on it.

Cheers,
Michujo.

Haha, maybe you were more naughty as a kid ;)

OK, thank you, i will have a try.
Steven.