Think of the air passing
over the wing as two regimes. One is the free stream air. Passing over a
cambered wing this will speed up - Bernouilli
The other regime is the
boundary layer where drag from the surface has slowed the air down. This also
exists in two different forms.
The laminar boundary
layer, the one at the front of the wing is smooth and thin. Inside it the speed
of the air reduces smoothly from the free stream value to near zero at the
surface. Because of this regular reduction in speed the average speed inside
the layer is about half the free stream value, and this fact, and the fact that
the layer is very thin mean that the total kinetic energy inside the layer is
relatively small.
The turbulent layer is
thicker and the turbulence pulls down free stream air deep into the layer. This
has two results. One is that the turbulent layer has more kinetic energy and
the other is that near the surface the airflow slows down very rapidly, causing
more drag. Drag is bad, but kinetic energy is good for the turbulent layer
punches through problems and keeps the airflow attached to the wing as you get
nearer the stall.
In summary, the turbulent
layer is thicker, has a higher mean speed within the layer, more drag but more
internal energy