Vortex Dynamics of Free-to-Roll Slender and Nonslender Delta Wings

摘要

Experiments were conducted on various free-to-roll delta wings with sweep angles in the range of 40–70 deg in anwind tunnel. For low sweep angles, nonzero trim angles are observed until the wing stalls after which the trim anglenbecomes zero. Themagnitude of the roll trimangle decreases with increasing sweep angle and almost disappears fornthe most slender wing. In a certain range of sweep angles, and just before the stall, large amplitude self-induced rollnoscillations with nonzero mean were observed for thin wings with sharp leading edges for which separation point isnfixed. Two different regions of angle of attack with free-to-roll oscillations were found for certain sweep angles.nVelocitymeasurements suggest that the oscillations are initiated by the increasing proximity of the shear layers as thenangle of attack is increased. Possiblemechanisms of the self-induced roll oscillations based upon the phase-averagednvelocitymeasurements have been proposed, incorporating varying vortex size and strength as well as themovementnof the shear-layer reattachment locations. Hysteresis and time lag effects are significant even though typicalndimensionless frequencies are very low.