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Outlet Boundary condition for Additional Variable

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Old   June 29, 2012, 06:20
Default Outlet Boundary condition for Additional Variable
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Ftab
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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.

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Ftab
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Old   June 29, 2012, 08:05
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Glenn Horrocks
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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.
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Old   September 20, 2012, 00:42
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Quote:
Originally Posted by ftab View Post
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?
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Old   September 20, 2012, 05:36
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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.
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Old   September 20, 2012, 07:31
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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.
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Old   September 21, 2012, 20:07
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Originally Posted by ghorrocks View Post
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.
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Old   September 22, 2012, 01:47
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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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