Developer's-corner/Boundary-Conditions.md

@@ -20,16 +20,21 @@ Disk {
 ```
 
 **FargOCA** will then invoke those boundaries condition at predefined place in the code. 
-The code has one ghost layer in each direction.
+The computational grid has one ghost layer in the radial and in the vertical direction . When running
+2D simulations only one boundary condition is required (radial)
+while for the 3D case it is necessary to provide a boundary condition for the colatitude (the layer at the disk surface). 
+When a 3D simulation is done by considering only one disk hemisphere (in case of vertical symmetry) a suited mirror boundary
+at the midplane is automatically used by the code. The vertical boundary condition will be applied at $`\phi =`opening 
  The aim of boundary 
 condition is to provide a value for the whole set of hydrodynamical
 quantities into the ghost layers.
 Possible boundaries are: 
 1. ``open`` valid both for 2D and 3D disc. An open boundary will
 let the gas flowing out at the innermost and outermost radial
-gridcell by copying the density of the first active gridcell
-into the ghost cell. 
-2. reflectingR and reflectingZ are commonly used boundaries.
+gridcell by copying the density of the first active layer
+into the ghost one. The sign of the radial velocity controls the
+outflow condition.
+2. ``reflectingR`` and ``reflectingZ`` (3D case only) are commonly used boundaries.
 All the quantities are copied from the active cell