Editing Boundary layer (section)

==Types of boundary layers==
[[Image:Boundarylayer.png|343x343px|thumb|right|Boundary layer visualization, showing transition from laminar to turbulent condition]]
Laminar boundary layers can be loosely classified according to their structure and the circumstances under which they are created. The thin shear layer which develops on an oscillating body is an example of a [[Stokes boundary layer]], while the [[Blasius boundary layer]] refers to the well-known [[Similitude (model)|similarity]] solution near an attached flat plate held in an oncoming unidirectional flow and [[Falkner–Skan boundary layer]], a generalization of Blasius profile. When a fluid rotates and viscous forces are balanced by the [[Coriolis effect]] (rather than convective inertia), an [[Ekman layer]] forms. In the theory of heat transfer, a thermal boundary layer occurs. A surface can have multiple types of boundary layer simultaneously.

The viscous nature of airflow reduces the local velocities on a surface and is responsible for skin friction. The layer of air over the wing's surface that is slowed down or stopped by viscosity, is the boundary layer. There are two different types of boundary layer flow: laminar and turbulent.<ref>{{cite book|last1=Young|first1=A.D.|title=Boundary layers|date=1989|publisher=American Institute of Aeronautics and Astronautics|location=Washington, DC|isbn=0930403576|edition=1st publ.}}</ref>

'''Laminar boundary layer flow'''

The laminar boundary is a very smooth flow, while the turbulent boundary layer contains swirls or "eddies." The laminar flow creates less skin friction drag than the turbulent flow, but is less stable. Boundary layer flow over a wing surface begins as a smooth laminar flow. As the flow continues back from the leading edge, the laminar boundary layer increases in thickness.

'''Turbulent boundary layer flow'''

At some distance back from the leading edge, the smooth laminar flow breaks down and transitions to a turbulent flow. From a drag standpoint, it is advisable to have the transition from laminar to turbulent flow as far aft on the wing as possible, or have a large amount of the wing surface within the laminar portion of the boundary layer. The low energy laminar flow, however, tends to break down more suddenly than the turbulent layer.