Chapter 9 : Laminar Boundary Layers
Lecture 28 :

 Boundary Layer Coordinates The boundary layer equations derived are in Cartesian coordinates. The Velocity components u and v represent x and y direction velocities respectively. For objects with small curvature, these equations can be used with - x coordinate : streamwise direction y coordinate : normal component They are called Boundary Layer Coordinates. Application of Boundary Layer Theory The Boundary-Layer Theory is not valid beyond the point of separation. At the point of separation, boundary layer thickness becomes quite large for the thin layer approximation to be valid. It is important to note that boundary layer theory can be used to locate the point of seperation itself. In applying the boundary layer theory although U is the free-stream velocity at the outer edge of the boundary layer, it is interpreted as the fluid velocity at the wall calculated from inviscid flow considerations ( known as Potential Wall Velocity) Mathematically, application of the boundary - layer theory converts the character of governing Navier-Stroke equations from elliptic to parabolic This allows the marching in flow direction, as the solution at any location is independent of the conditions farther downstream.