LATERAL OSCILLATIONS OF AN AIRCRAFT MODEL AT HIGH ANGLES OF ATTACK

Lateral oscillations occurring on the aircraft model of NASA TP 1803 a t angles of attack ranging from 25 degrees to 60 degrees have been inv estigated in a low-speed wind tunnel for configurations including fuse lage with wing or with a combination of wing and leading-edge extensio n (LEX). The wind tunnel experiment was conducted in the range of Mach number from 0.1 to 0.2, and the range of the Reynolds number based on the body diameter from 2.8 x 10(5) to 5.6 x 10(5). The time-varying s ide force coefficients, which may represent the displacements of oscil lation in the lateral direction, were measured to obtain the root-mean -square values and the power spectra. mow visualization of the vortice s generated from the forebody, wing and LEX of the model has also been performed in a water tunnel. It was found that the entire system of t he flow and the sting-supported model locks-in at the resonant oscilla tion frequency as the lateral oscillation occurs. The presence of LEX significantly enhances the oscillation amplitude especially at high en ough angles of attack, i.e., alpha > 40 degrees. The enhancement of th e lateral oscillation, as suggested by the water tunnel visualization, seems closely related to the breakdown of the LEX vortices in general and the location of breakdown in particular. The power spectra of the test model with wind and LEX exhibit a transition from weakly nonline ar to broad band oscillations as alpha is increased from 45 degrees to 60 degrees. The appearance of a broad range of frequencies around or below the dominant frequency, that can be indicative of possible chaot ic oscillation, corresponds to a sharp drop of the lateral oscillation amplitude. The effect of Reynolds number is notable only at alpha > 5 0 degrees. Variation of the sideslip angle between 0 and 10 degrees ap pears to have no discernible effects on the amplitude of lateral oscil lation for the test model with wing and LEX. (C) 1996 Academic Press L imited