Developer's-corner/Boundary-Conditions.md

@@ -20,7 +20,17 @@ Disk {
 ```
 
 **FargOCA** will then invoke those boundaries condition at predefined place in the code. 
-<!-- Might want to develop -->
+The code has one ghost layer in each direction.
+ 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.
+All the quantities are copied from the active cell  
 
 
 ## Adding new boundaries conditions