AIAA Paper 97-2266, 15th AIAA Applied Aerodynamics Conference, June 23-25, 1997

"Reduction of Narrow-Band Velocity Fluctuations Over an Aircraft Model "

M. A. Klein and N. M. Komerath

ABSTRACT:  Surface fences are used to reduce the narrow-band velocity fluctuations observed over a 1/32-scale model of an F-15 at high angles of attack in a low speed wind tunnel. Previous work has traced these fluctuations to counter-rotating structures in the shear layer above the wing surface. A small vertical fence placed near the origin of the fluctuations attenuates the peak spectral energy by as much as 67% at 21.5° angle of attack. A narrow region is identified on the wing surface where fence placement attenuates the spectral peak, and fence size is optimized. A single fence location is identified where attenuation is achieved for angles of attack ranging from 16° to 34°. Comparisons with flight test accelerometer data confirm that the frequencies of significance to tail buffeting are the ones predicted in scaled model tests and attenuated by this technique. These results show that focusing on the surface shear layer, rather than on core instabilities, enables the engineer to take results obtained on small-scale wings and arrive at the optima found by trial and error on models with aeroelastic tails, and apply them to full-scale aircraft.

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