HUGE change in results between opening and inlet

gwheeler · October 30, 2013, 10:45

I'm struggling to understand the difference between an opening and inlet boundary condition. I ran my model of a tube transporting hot gas and cooled by convection of the surrounding air domain. I tried changing one wall of the surrounding air domain from opening to inlet (in both cases I set the boundary temp and pressure the same). I get a really big difference in the resulting temperature drop of the hot gas. Can anyone explain why, and which boundary condition is more appropriate?

Thanks,
Greg

keeper · October 30, 2013, 11:23

even if it could be unreliable, have you tried static pressure on both cases as the BC?

gwheeler · October 30, 2013, 11:49

Yes, no significant difference in either case when I specify static pressure. Still a huge difference between the two cases.

keeper · October 30, 2013, 12:22

you could try to extend both ends of BCs (inlet, outlet)

ghorrocks · October 30, 2013, 16:58

Have you looked at the velocity vectors? I bet the flow is totally different in the two cases.

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October 30, 2013, 11:23		#2
keeper Senior Member Join Date: Jul 2010 Posts: 152 Rep Power: 15	even if it could be unreliable, have you tried static pressure on both cases as the BC?

October 30, 2013, 11:49		#3
gwheeler New Member Greg Join Date: May 2011 Location: Boise, ID Posts: 3 Rep Power: 14	Yes, no significant difference in either case when I specify static pressure. Still a huge difference between the two cases.

October 30, 2013, 12:22		#4
keeper Senior Member Join Date: Jul 2010 Posts: 152 Rep Power: 15	you could try to extend both ends of BCs (inlet, outlet)

October 30, 2013, 16:58		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,697 Rep Power: 143	Have you looked at the velocity vectors? I bet the flow is totally different in the two cases.