Outlet Boundary condition for Additional Variable

ftab · June 29, 2012, 06:20

Hi all,
Making the BC for additional variable which is transported by transport equation in incompressible subsonic flow, I can find seperate box in Inlet BC specification dialogue tab, but not in the outlet.
The outlet only asks for the main flow and not for the additional variable. Ho w I should set for instance constant value or flux at the outlet?
I do not think that using the source tab, and setting the source flux to zero would be a good option.

Thanks,
Ftab

ghorrocks · June 29, 2012, 08:05

No, setting a source flux to zero would not be a good option

It does not ask for a AV boundary condition as none is required. The AV simply convects out of the domain so no boundary condition is required.

Aisun · September 20, 2012, 00:42

Quote:

Originally Posted by ftab

Hi all,
Making the BC for additional variable which is transported by transport equation in incompressible subsonic flow, I can find seperate box in Inlet BC specification dialogue tab, but not in the outlet.
The outlet only asks for the main flow and not for the additional variable. Ho w I should set for instance constant value or flux at the outlet?
I do not think that using the source tab, and setting the source flux to zero would be a good option.

Thanks,
Ftab

I want to know the method to set the outlet condition to the additional variable, too. Do you know how to do it?

ftab · September 20, 2012, 05:36

Quote:

Originally Posted by Aisun

I want to know the method to set the outlet condition to the additional variable, too. Do you know how to do it?

So far no, as Ghorrocks said there is no BC needed since it is simply convected away. Fluent used to have BC for it though.

ghorrocks · September 20, 2012, 07:31

It is available for openings are flow can enter the domain from an opening and the solver needs to know what AV value to assign it. But as the flow can only exit an outlet there is no need to give boundary conditions to the AV.

evcelica · September 21, 2012, 20:07

Quote:

Originally Posted by ghorrocks

It is available for openings are flow can enter the domain from an opening and the solver needs to know what AV value to assign it. But as the flow can only exit an outlet there is no need to give boundary conditions to the AV.

Exactly, the fluid leaves the domain, an additional variable boundary condition would be meaningless.

mp121209 · September 22, 2012, 01:47

You must know how to make BC for a subsonic flow case. Since all Riemann's invariants are considered, there must be 4 variables specified at the inlet, only and must be one at the outlet. Say, for example, you can specify u,v,w,p and T and the outlet.

June 29, 2012, 06:20	Outlet Boundary condition for Additional Variable	#1
ftab Member Ftab Join Date: Sep 2011 Posts: 87 Rep Power: 14	Hi all, Making the BC for additional variable which is transported by transport equation in incompressible subsonic flow, I can find seperate box in Inlet BC specification dialogue tab, but not in the outlet. The outlet only asks for the main flow and not for the additional variable. Ho w I should set for instance constant value or flux at the outlet? I do not think that using the source tab, and setting the source flux to zero would be a good option. Thanks, Ftab

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June 29, 2012, 08:05		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,696 Rep Power: 143	No, setting a source flux to zero would not be a good option It does not ask for a AV boundary condition as none is required. The AV simply convects out of the domain so no boundary condition is required.

September 20, 2012, 07:31		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,696 Rep Power: 143	It is available for openings are flow can enter the domain from an opening and the solver needs to know what AV value to assign it. But as the flow can only exit an outlet there is no need to give boundary conditions to the AV.

September 22, 2012, 01:47		#7
mp121209 New Member Trần Đình Thắng Join Date: Mar 2012 Location: Moscow Russia, Hanoi Vietnam Posts: 24 Rep Power: 14	You must know how to make BC for a subsonic flow case. Since all Riemann's invariants are considered, there must be 4 variables specified at the inlet, only and must be one at the outlet. Say, for example, you can specify u,v,w,p and T and the outlet.