Suppression of Wing Rock in Slender Delta Wing by Horizontal Strakes

The experimental investigations of this paper show that delta- and reverse-delta-shaped small horizontal strakes (fineness ratio of 3-5%) are capable of suppressing the wing rock of a slender delta wing above 35deg angle of attack. The parametric study reveals that 45deg sweepback and sweepforward angles are the most favorable combinations, while the most advantageous streamwise location of the strake is the beginning of the delta wing. The suppression capability is also evident during pitching up, but no significant deterioration of the lift-to-drag ratio is observed. The suppression is achieved by changes in the vortical flowfield brought in by the strakes. During a roll, the strake 1)alters the away normal and outward spatial location of the up-going semispan's vortex to closer normal and inward spatial location, respectively, and 2)reduces the difference in the normal distances of vortices of two semispans, both of which are the characteristics of no-wing-rock regime, such as 15deg angle of attack. Thus, the strake changes the asymmetric flow to nearly symmetric. Such change in the vortical flowfield is caused by the interaction of two vortices emanating from the strake, with the vortex pair originating from the delta wing.