On the unsteady flows generated by impulsive motion of a boundary

Some properties of unsteady unidirectional flows of viscous fluids are examined for flows impulsively started from rest by the motion of a boundary or two boundaries. Three illustrative examples are given. The first example is the unsteady Couette flow, the second is the unsteady flow between two parallel plates suddenly set in motion with the same speed and the third is the unsteady flow in a circular cylinder moving parallel to its length. It is shown that if the conditions for which the values of the quantities such as velocity, flux and skin friction obtained for large times are nearly the same with those obtained for small times are established, the expressions of the quantities obtained for one of large times or small times can also be used for the other.