use_custom_prob.md

@@ -29,22 +29,25 @@ pbl.add(dart.Freestream(msh, 'freestream', dim, alpha, beta = 0))
 where `'freestream'` is the name of the physical group of the mesh containing the elements belonging to the boundary onto which the Freestream condition will be enforced. In all the cases, `beta` can be omitted if it is zero.  
 Note that the downstream boundary of the domain MUST ALWAYS be assigned a Freestream boundary condition since it will intersect a wake. Also note that zero mass flux boundary conditions are naturally enforced by the FEM. The slip boundary conditions hence do not require to be explicitly added on bodies immersed in the flow.
 
-**2.3 Adding the Kutta condition**  
-A Kutta condition must be added to allow lifting configurations to generate aerodynamic loads. For a 2D flow, both the dart::Wake and dart::Kutta classes need to be used as,
+**2.3 Adding wake boundary conditions and the Kutta condition**  
+Two additional conditions must be prescribed to allow lifting configurations to generate aerodynamic loads. Firstly, boundary conditions must be enforced on wake surfaces and secondly, the Kutta condition needs to be enforced on the trailing edge of any lifting surfaces. For 2D flows, the wake boundary conditions are added using the dart::Wake class as,
 ```python
 pbl.add(dart.Wake(msh, ['wake', 'wake_', 'field']))
-pbl.add(dart.Kutta(msh, ['te', 'wake_', 'body', 'field']))
 ```
-where `'wake_'` is the physical group of the mesh containing the lower wake elements, and is automatically created by tbox::MshCrack, and `'te'` is the name of the physical group of the mesh containing THE point element defining the trailing edge of `'body'`. Note that the wake surface does not need to be aligned with trailing edge bissector for 2D flows because dart::Kutta adds a supplementary term on the elements touching the trailing edge that correctly computes the local flow direction.  
-For 3D flows, only the dart::Wake class is used,
+where `'wake_'` is the physical group of the mesh containing the lower wake elements, and is automatically created by tbox::MshCrack. For 3D flows, an additional parameter is required, and the use of dart::Wake slightly differs,
+```python
+pbl.add(dart.Wake(msh, ['wake', 'wake_', 'field', 'tips']))
+```
+where `'tips'` is the physical group of the mesh containing the edge boundaries of the wake to be excluded from the formulation (no contributions will be added to the nodes belonging to this group). This group includes the free edge of the wake for wings and tails. Additionally, if a fuselage is considered, it should also include the intersection of the wake with the fuselage.  
+The Kutta conditions is added using the dart::Kutta for both 2D and 3D flows,
 ```python
-pbl.add(dart.Wake(msh, ['wake', 'wake_', 'field', 'teTip']))
+pbl.add(dart.Kutta(msh, ['te', 'wake_', 'body', 'field']))
 ```
-where `'teTip'` is the physical group of the mesh containing the trailing edge of the lifting configuration AND the free edge of the wake (no contributions will be added to these nodes). Since dart::Kutta cannot be used for 3D flows, the wake surface MUST be aligned with the trailing edge bissector in order to yield consistent results.
+where `'body'` is the name of the physical group of the mesh containing the element of the body surface on which the wake is attached, and `'te'` is the name of the physical group of the mesh containing the elements defining the trailing edge of `'body'`. Note that the wake surface does not need to be aligned with trailing edge bissector because dart::Kutta adds a supplementary term on the elements touching the trailing edge that correctly computes the local flow direction.
 
 **2.4 Adding bodies immersed in the fluid**  
 A lifting body can be added by using the dart::Body class as,
 ```python
 pbl.add(dart.Body(msh, ['body', 'field']))
 ```
-where `'body'` is the name of the physical group of the mesh contaning the element of the body surface. This will allow the computation of the aerodynamic load coefficients on this body, as well as further data manipulation, e.g. for fluid-structure interaction or optimzation problems.
+This will allow the computation of the aerodynamic load coefficients on this body, as well as further data manipulation, e.g. for fluid-structure interaction or optimzation problems.