Formation of vortices on a tubercled wing, and their effects on drag

Wake surveys of 2 swept NACA 0021 wings were conducted at angles of attack of 0°, 3°, 6°, 9°, and 12°. One wing had a smooth leading edge and the other had a tubercled leading edge. Sweeping the tubercled wing resulted in one vortex in each vortex pair being at least 4 times stronger than the other. There was little difference between the strength of the wingtip vortices of either wing at 3°. From 6° onwards tubercles reduced the strength of the wingtip vortex. The tubercle troughs tended to produce local maxima and minima in the profile and induced drag coefficients, respectively. The converse was true over the peaks. The change in the profile, induced, and total drag coefficients primarily arose from over the wingspan; there was little contribution from the wingtip region.