boundary conditions
Dear friends, My question is very simple. If in a numerical problem a symetry exists, so when we are treating a node on the symertic axis we will consider all the heat flux (in and out) the control volume surrounding the node as equal to zero. Is it correct or no?? Is true even if we take half of the calculation domain?? thanx for ur contribution

Re: boundary conditions
(1). The symmetry condition simply says that the solution is symmetric with respect to the symmetry axis, or symmetry plane. Only at that particular location. (2). The other way to say is that the solution has a zero gradient normal to the symmetry axis at that point. (3). How you place the cell at the boundary is a different story. For conduction, with the temperature gradient equal to zero at the symmetry axis, there is no heat transfer at that location normal to the axis. (4).For a typical control volume, you will have three other surfaces for 2D and 5 other surfaces for 3D cases. The symmetry condition controls only one surface, not all surfaces.

Re: boundary conditions
The heat flux through a certain face will be zero only if the face is contained in the plane of symmetry (is a part of it).
If you have a node (and not a face of the control volume) on the symmetry plane then the heat flux is not neccessary zero in the faces of the control volume. I any Basic Book of CFD is the proper treatment of the boundary in such case ( see Patankar for instance) 
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