The effects of apex flap on the leading-edge vortex breakdown of a cropped double delta wing

The dye-injection flow visualisation technique was used to investigate the effect of the apex flap on the leading-edge vortex breakdown over a cropped 76°/40° double delta wing. The angle-of-attack of the experimental model varied from 20° to 40°, and the length of the apex flap was 25%c and 50%c respectively. By changing the angle of the apex flap, we found that the apex flap is an efficient method to control the leading-edge vortex breakdown, and that there exists an angle of the apex flap at which the value of the leading-edge vortex breakdown delay reaches maximum. Moreover, it is found that, for α <28°, the small apex flap is a better choice for delaying the vortex breakdown; for α > 28°, the large apex flap is superior to the small one.