Unsteady boundary layers close to the stagnation region of slender bodies

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Abstract
The evolution of unsteady boundary layers on the plane of symmetry of a slender prolate spheroid in uniform motion at constant angle of attack after an impulsive start has been studied for the case of a prescribed pressure distribution. Calculated results have been obtained for angles of attack ranging from 30° to 50° and show, for example, that the unsteady-state solutions approach the steady-state solutions rapidly on the windward and leeward sides for α < αc (≈ 41°). This is also so on the windward side for α > αc. On the leeward side for α > αc, however, the unsteady boundary layer is initially unseparated, but develops a region of reversed flow with increasing time. Subsequently, the streamwise displacement thickness develops a pronounced peak, which leads to a singularity of the type observed by van Dommelen & Shen on a circular cylinder started impulsively from rest.

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