Consider the growth of the boundary layer over an aerofoil placed at high incidence, the potential flow pressure distribution of which is shown in Fig. 1. In the region AB, the flow will normally remain laminar because of the large favourable gradient, but after reaching the peak B, instability will begin. Depending on the Reynold's number and the actual adverse gradient, the boundary layer will do one of three things:

1. 1. It will separate from the surface while still remaining laminar;

2. 2. It will become turbulent (transition) and will remain on the surface, or;

3. 3. It will become turbulent and will separate from the surface a little later.