Effects of sinusoidal leading edge on delta wing performance and mechanism

Lift and drag characteristics of delta wings with low swept angle and various sinusoidal leading edges (SLE) were investigated in a wind tunnel. Three amplitudes and three wavelengths of SLE were tested. It is revealed that, in comparison with the baseline case, when the leading-edge amplitude Aa (c) 1/25%C (root chord length of a delta wing), the stall of the delta wing can be delayed without penalty on the maximum lift coefficient; meanwhile, the lift-to-drag ratio was kept nearly unchanged. These are beneficial to aircraft maneuverability and agility. Surface oil and hydrogen-bubble flow visualization experiments were further conducted to provide a general view of the underlying flow mechanism of SLE on delta wings. It was found that, for the flow over delta wing with SLE, vortices were generated from every crest of SLE, in contrast to the dual leading-edge vortex structure generated from the apex of the base wing. At high angle of attack, the breakdown of those vortices originating from the crests of SLE may provide additional turbulent kinetic energy to the flow, resulting in the increase of the flow reattachment region on the leeward side, therefore the stall can be delayed.