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-   -   Outlet Boundary condition for Additional Variable (http://www.cfd-online.com/Forums/cfx/103928-outlet-boundary-condition-additional-variable.html)

ftab June 29, 2012 06:20

Outlet Boundary condition for Additional Variable
 
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

hello
 
Quote:

Originally Posted by ftab (Post 368868)
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 (Post 382680)
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 (Post 382746)
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.


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