Unsteady Laminar Boundary Layers

Abstract

The purpose of this article is to review recent developments of certain aspects of the theory of unsteady laminar boundary layers. The review is not all-embracing in the sense that the theory of unsteady boundary layers in rotating fluids is touched upon only briefly, and the theory of hydrodynamic stability is ignored completely. We are concerned, for the most part, with the motion of a bluff body and a semi-infinite plate. Thus we consider the impulsive motion of a cylinder perpendicular to its generators (§ 3) , and review current ideas concerning unsteady boundary layer separation. We also consider (§ 4) the corresponding problem for a semi-infinite flat plate, for which a complete description of the flow is now available, together with the related problem which arises when such a plate is placed in a uniform stream upon which is superposed an harmonic fluctuation. Finally (§ 5) we consider the flow induced when a bluff body performs small-amplitude oscillations in a fluid which is otherwise at rest.