AE 3005 HANDOUT #4

AE 3005 HANDOUT #4

Important Features of Prandtl's Boundary layer Theory

The 2-D steady, incompressible laminar boundary layer equations are:

The 2-D steady, compressible boundary layer equations are:

Some observations are:

a) The variation of pressure across the boundary layer is small. Thus, we can assume that pressure varies only with respect to x. The pressure field may, therefore, be computed at the edge of the boundary layer from inviscid flow theories, without any knowledge of the boundary layer characteristics.

b) The v- component of velocity within the boundary layer is of the order of O(V∞d/c) where d is the boundary layer thickness.

c) The boundary layer thickness d is very small, and for laminar flows it varies inversely as the square root of Reynolds number rV∞c/m.

d) We will assume the airfoil surface to be flat, and use a Cartesian coordinate system, neglecting surface curvature. This is because the boundary layer thickness d is very small compared to the airfoil surface radius of curvature.