Effects of Time Scales on Lift of Airfoils in an Unsteady Stream

Ismet Gursul*, Hank Lin†, and Chih-Ming Ho‡

*Assistant Professor, Department of Mechanical, Industrial, and Nuclear Engineering, University of Cincinnati.

†Research assistant, Department of Aerospace Engineering, University of Southern California.

‡Professor, Mechanical, Aerospace, and Nuclear Engineering Department, University of California, Los Angeles.

Abstract

In unsteady aerodynamics, the reduced frequency has always been considered as the predominant controlling parameter because it relates to the unsteadiness. In this study, we examined the responses of several delta wings of varying aspect ratio and a two-dimensional wing in an unsteady periodic freestream. We found that in certain operating conditions, the lift of the airfoils may or may not be a function of the reduced frequency, depending on whether the leading-edge separation vortex can remain stationary on the wing or not. For delta wings with attached, stationary leading-edge vortices, the lift forces are not a function of the reduced frequency. However, if the leading-edge vortices shed and convect downstream, then the lift force depends on the reduced frequency.

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