On the unsteady unidirectional flows generated by impulsive motion of a boundary or sudden application of a pressure gradient

Some exact solutions of the time-dependent Navier-Stokes equations are discussed for flows impulsively started from rest by the motion of a boundary or two boundaries or by sudden application of a pressure gradient. It is shown that the expressions of the quantities such as velocity, flux and skin friction obtained in a series form for large times can also be used to find their values for small times or vice versa. Furthermore, conditions for which the values of the quantities at large times are nearly the same with those at small times are derived.