• It states that the u component of velocity with two velocity profiles of u(x,y) at different x locations differ only by scale factors in u and y . 
  
• Therefore, the velocity profiles u(x,y) at all values of x can be made congruent if they are plotted in coordinates which have been made dimensionless with reference to the scale factors.
  
• The local free stream velocity U(x) at section x is an obvious scale factor for u, because the dimensionless u(x) varies between zero and unity with y at all sections.
  
• The scale factor for y , denoted by g(x) , is proportional to the local boundary layer thickness so that y itself varies between zero and unity.
  
• Velocity at two arbitrary x locations, namely x₁ and x₂ should satisfy the equation
  

  (28.17)

• Now, for Blasius flow, it is possible to identify g(x) with the boundary layers thickness δ we know

Thus in terms of x we get                                   

i.e.,                                                                   

(28.18)

where       
or more precisely,

	(28.19)

The stream function can now be obtained in terms of the velocity components as

or

(28.20)

where D is a constant. Also  and the constant of integration is zero if the stream function at the solid surface is set equal to zero.

Now, the velocity components and their derivatives are:

(28.21a)

                 or     

(28.21b)

(28.21c)

(28.21d)

(28.21e)

Substituting (28.2) into (28.15), we have

 

 

or,

where	(28.22)
and

This is known as Blasius Equation .