We have four conditions that a proposed velocity profile should satisfy: u=0 u = U. at y = 0 at y = 8 0 11 at y = 8 (8.6.9) ди ду au ay" 0 at y = 0 The first three of these conditions are obvious from a sketch of a velocity profile; the fourth condition comes from the x-component Navier-Stokes equation (5.3.14) since u = v= 0 at the wall, a'ulax? = 0 on the wall, and dp/dx = 0 for the steady flow on the flat plate under consideration.