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-   -   convective boundary condition (http://www.cfd-online.com/Forums/cfx/25102-convective-boundary-condition.html)

Mani January 25, 2008 09:08

convective boundary condition
 
Hi

Can anyone tell me what on earth is convective boundary condition and how can i impose it at the outlet of my model. Thanks

Mani

Glenn Horrocks January 28, 2008 18:24

Re: convective boundary condition
 
Hi,

It is normally used on a wall boundary condition to model heat transfer from the wall. It is not usually used at outlets.

Glenn Horrocks

Mani January 28, 2008 18:36

Re: convective boundary condition
 
Well in the paper that i have infront of me they have imposed this BC at the outlet. How can i use it in CFX anyway.

Mani

Glenn Horrocks January 29, 2008 19:33

Re: convective boundary condition
 
Hi,

I have no idea. I can't see how imposing a convective heat transfer condition on an outlet can have any physical basis. The fluid exiting an outlet depends on the temperature upstream.

Glenn Horrocks

Glenn Horrocks January 29, 2008 19:34

Re: convective boundary condition
 
Are you sure they were not applying a thermal radiation boundary condition? You can apply this type of boundary on an outlet in CFX.

Glenn Horrocks

Andreas January 30, 2008 04:29

Re: convective boundary condition
 
Convection means something (mass, momentum, heat, concentration) is transported by the fluid; this is described by the term "div(rho u Phi)" where rho is density, u is velocity and Phi is what is transported. CFX has this convective boundary condition at outlets: for mass and momentum if you set pressure there, and for heat and concentrations this is automatically set (you cannot choose e.g. a temperature at an outlet). There comes a difficulty if pressure fluctuations reach the outlet since they can be reflected there so that the outlet is not fully "convective"; for this, try the beta feature "non-reflecting boundary conditions".

Mani January 30, 2008 07:13

Re: convective boundary condition
 
Thank you Glenn & Andreas. How can i use "non-reflecting boundary condition" which i suppose is same as "convective BC". The purpose in either case would be to prevent pressure fluctuations reflecting back in flow domain right.

Mani

Mani February 2, 2008 17:25

Re: convective boundary condition
 
Ok i understand now what you meant Andreas. Thank you

Mani


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