The flow outside of the boundary layer reacts to the shape of the edge of the boundary layer just as it would to the physical surface of an object. So the boundary layer gives any object an "effective" shape that is usually slightly different from the physical shape. The boundary layer may also lift off or separate from the body, creating an effective shape much different from the physical shape of the object and causing a dramatic decrease in lift and increase in drag. When this happens, the airfoil has stalled.
As well as the development of airfoil stall, the details of the flow within the boundary layer are very important for many problems in aerodynamics, including the skin friction drag of an object and the heat transfer that occurs in high-speed flight.
The theory that describes boundary layer effects was first presented by Ludwig Prandtl in the early 1900s. Prandtl was the first to realize that the forces experienced by a wing increased from the layer very near the wing's surface to the region far from the surface.
Adapted from the US Centennial of Flight Commisssion, History of Flight website
Related category AERODYNAMICS AND AERONAUTICS
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