Ask A Scientist© Engineering Archive

Index Key:   ENG025
Author:      wildman jackson
Subject:     Boundary layers
Text:        What exactly is a boundary layer, and what relationship does it 
have to planes?

Response #:  1 of 1
Author:      proach
Text:        When a solid body moves through a fluid such as air, there is a 
thin layer next to the surface of the body where the fluid moves with the 
body.  There is no slip of the fluid with respect to the body in this thin 
layer.  At greater distances from the surface, there is some slip, and the 
fluid is dragged along at some speed between that of the body and the 
stationary mass of fluid.  This layer, in which the fluid is being dragged by 
the body, is the boundary layer.  The behavior of this boundary layer is very 
important in determining such things as the drag force on the body.  At high 
speeds, such as with an airplane, the drag force can be very large.  
Understanding what the boundary layer is doing can help to reduce this force.