On boundary layers associated with oscillating streams

Summary

The paper gives a description of the effects which are produced in laminar boundary layers by the presence of oscillations in the free stream. These are two in number. First, the external oscillations induce oscillations in the boundary layer itself; the phases of the oscillations at different distances from the wall in the boundary layer are shifted with respect to each other and to the forcing oscillation. This is a purely viscous effect. Secondly, the oscillation occurs about a different mean profile from the steady state profile which would correspond to the average external velocity. The latter effect is equivalent to a secondary flow. It is lost in a mathematical analysis in which the inertia terms are neglected and depends, therefore, on an interplay between the inertia and viscous forces.

The paper also contains a series solution for the skin friction coefficient on and rate of heat transfer from a flat plate in a uniform stream on which there is superimposed a harmonic oscillation progressing with a velocity equal to the mean velocity of flow.