On the separation of the unsteady laminar boundary layer

Abstract

When a boundary layer is subjected to unsteady conditions, it strongly tends, if it is thin, to be quasi-steady; that is, to be described at each instant by the appropriate steady equations of motion. In many cases of practical interest a thin boundary layer is nearly quasi-steady, but, owing to some imposed unsteadiness, its departures from quasi-steadiness require estimation. Such is the case during rotating stall in an axial flow compressor and stalling flutter of an airfoil. In these problems, any essential unsteadiness in the boundary layer tends to produce a hysteresis in the relation between lift and angle of attack, thus affecting the energy balance of the flow oscillation. In this connection, of course, the unsteady features of separation must be accounted for, at least approximately, in any attempt to predict consequences of unsteadiness of the airfoil boundary layer. It is the particular problem of separation to which the present paper is addressed.

The present paper is based on analyses conducted under the sponsorship of the U.S. Air Force through the Office of Scientific Research and through the Aeronautical Research Laboratory of the Wright Air Development Center.