Some Important Problems in Unsteady Boundary Layers Including Separation. II. Unsteady Boundary Layers Close to the Stagnation Region of Slender Bodies

摘要

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 prescribed pressure distribution. Calculated results have been obtained for angles of attack ranging from 30 degrees to 50 degrees and show, for example, that the unsteady-state solutions approach the steady-state solutions rapidly on the windward and leeward sides for alpha < and alpha sub c (approximately - 41 degrees). This is also so on the windward side for alpha > alpha sub c. On the leeward side for alpha > and alpha sub c, 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 and Shen on a circular cylinder started impulsively from rest. (Author)