What is the boundary layer (aerofoils)?

[BlueCB]

Can someone please explain to me the nature of the boundary layer and its effects on fluid flow over an aerofoil?

Thanks,

 

[boneh3ad]

When a fluid with nonzero viscosity (essentially any fluid) will tend to "stick to" the wall over which it is passing. This means that at the wall, the velocity is zero relative to the wall. For any fluid moving relative to the wall, there will be some region where the velocity of the fluid transitions smoothly from zero at the wall up to the free-stream value far away from the wall. The region between the wall and the point where the fluid velocity assumes the velocity of the free stream is called the boundary layer.

 

[Anish Aravinth]

Boudary layer: As the name implies some meaning to this term (i.e)it is a thin layer where velocity gradients exists inside this layer. This velocity gradients exists because of the viscous effects between two adjacent streamlines. At the surface of the airfoil the velocity is zero which is referred to as "No slip condition". Above this boundary layer the velocity will be equal to the freestream velocity...You can find lots of papers and journals regarding BL...Just google it.

 

[Aero_UoP]

Definition from Schlichting's Boundary-Layer Theory:
Boundary Layer: A very thin layer in the immediate neighbourhood of the body in which the velocity gradient normal to the wall, θu/θy, is very large. In this region the very small viscosity, μ, of the fluid exerts and essential influence so far as the shearing stress τ=μ(θu/θy) may assume large values.