convergence problem for opening BC (entrainment)

kuhbuh · September 7, 2009, 13:23

Hello everyone!

I'm having convergence problem using opening BC with static pressure (entrainment) condition. My other BCs are inlet and outlet. My model is two-phase compressible. I've played around the automatic timescale and local timescale but I still have poor convergence. If I use inlet instead of opening-entrainment, my simulation converges. Do you have any suggestion guys? Entrainment BC is more suitable for my model. Thanks a lot!

ghorrocks · September 7, 2009, 21:50

The entrainment BC is much harder to converge so if you are having problems converging then I would not use it. It might be better to move your boundary further away so you can use the simpler non-entrainment boundaries.

kuhbuh · September 7, 2009, 22:04

Thanks a lot for the advice Sir Glenn! Do you think entrainment BC is more mesh sensitive than other BC? Thanks.

ghorrocks · September 8, 2009, 07:49

It probably is. It is certainly harder to converge in general than the normal BCs. That is why if possible I prefer to move the boundaries further away from the region of interest and use simpler BCs instead.

kuhbuh · September 9, 2009, 22:29

I got it sir. Thank you so much again!

September 7, 2009, 13:23	convergence problem for opening BC (entrainment)	#1
kuhbuh New Member Join Date: Jun 2009 Posts: 20 Rep Power: 17	Hello everyone! I'm having convergence problem using opening BC with static pressure (entrainment) condition. My other BCs are inlet and outlet. My model is two-phase compressible. I've played around the automatic timescale and local timescale but I still have poor convergence. If I use inlet instead of opening-entrainment, my simulation converges. Do you have any suggestion guys? Entrainment BC is more suitable for my model. Thanks a lot!

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September 7, 2009, 21:50		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	The entrainment BC is much harder to converge so if you are having problems converging then I would not use it. It might be better to move your boundary further away so you can use the simpler non-entrainment boundaries.

September 7, 2009, 22:04		#3
kuhbuh New Member Join Date: Jun 2009 Posts: 20 Rep Power: 17	Thanks a lot for the advice Sir Glenn! Do you think entrainment BC is more mesh sensitive than other BC? Thanks.

September 8, 2009, 07:49		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	It probably is. It is certainly harder to converge in general than the normal BCs. That is why if possible I prefer to move the boundaries further away from the region of interest and use simpler BCs instead.

September 9, 2009, 22:29		#5
kuhbuh New Member Join Date: Jun 2009 Posts: 20 Rep Power: 17	I got it sir. Thank you so much again!