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Unsteady Flows Around Three-Dimensional Wings.

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Final technical rept. 1 May 83-30 Sep 84,

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Time-dependent flows around rectangular, swept or delta wings undergoing harmonic pitching motions were investigated using flow visualization techniques. The wings were towed in an 18-m water channel at chord Reynolds numbers up to 350,000. Fluorescent dye layers were excited with a sheet of laser light and used to mark the flow in the separation region around the lifting surface, the wake region and the potential flow away from the wing. The flow field around each wing depends to a large degree on wing planform, leading edge contour, and the reduced frequency of oscillation. The results can be mostly explained in terms of the mutual induction between the leading edge separation vortex and the trailing edge shedding vortex. For steady state flow around the delta wing constant angle of attack and constant speed, the present visualization experiments revealed the existence of a shear layer near the leading edge that rolls up and form discrete vortices parallel to the leading edge. These vortices were observed to pair at least once as they were convected downstream. Similar phenomena were observed in the unsteady case, except that the vortices shed from the leading edge were modulated and altered by the unsteady motion which was an order of magnitude lower in frequency. In general, the unsteadiness delayed separation and promoted hysteresis similar to results obtained in unsteady two-dimensional airfoils. Keywords include Unsteady separated flows Three-dimensional wings, Pitching wings, and Supermaneuverability.

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  • Fluid Mechanics

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