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