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

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

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

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

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

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".

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

Ok i understand now what you meant Andreas. Thank you

Mani

[Hamed1117]

non reflecting boundary condition in OpenFoam is almost the same to convective one,

see this link !

http://caefn.com/openfoam/bc-advective-wavetransmissive