An Investigation of Unsteady Stall Phenomenon on a Slender Elliptic Cylinder.

摘要

An investigation has been conducted to determine the lift hysteresis loops on a slender elliptic cylinder undergoing small amplitude angle of attack oscillations about some mean angle of attack. The results obtained in this investigation are briefly reviewed in this final report. The investigation was conducted in three phases. In the first phase the boundary layer over the cylinder was assumed to be entirely laminar. Simple lift hysteresis loops are obtained in this case and these hysteresis loops exhibit some of the same general characteristics as the lift hysteresis loops for airfoils oscillating in pitch. The second phase of the investigation involved a study of the nature unsteady boundary layer separation. Analytical solutions were obtained for the unsteady laminar boundary layer equations for several flows which approach separation. These solutions verify the Moore-Ratt-Sears model for unsteady boundary layer separation, at least for the case of upstream moving separation. It does not appear that solutions are possible for the case of downstream moving separation at this time. In the final phase of this investigation an attempt was made to determine the lift hysteresis loops for the case where the boundary layer on the cylinder is partially turbulent. It was found that a solution to this problem, by the solution technique proposed, is not possible at this time. (Author)