As long as this region remains thin then a number of approximations can be made that greatly simplify the equations. This idea has turned out to be an extremely powerful one, to the extent that a huge number of engineering flow calculations today are performed by combining an inviscid solution for the outer flow with a viscous boundary layer solutions to provide the flow near the body. The present applets implement several different boundary layer calculation methods. They can be solved directly by finite difference method. Techniques that use this second approach are termed 'integral methods'.
Boundary layers can be either laminar or turbulent.
Laminar boundary layers usually form near the leading edge or nose of a body. The flow in a laminar boundary layer is smooth and steady. The flow inside a turbulent boundary layer is unsteady and irregular and it is the time-averaged boundary layer equations that must be solved in this case. In a finite difference method an explicit turbulence model is used. In an integral method, the turbulence model is implicit in the assumed form of the velocity profile.