دانلود رایگان مقاله تشکیل گردابه در جناح برآمدگی و اثرات آنها بر درگ

ABSTRACT

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.

4. Conclusion

Wake surveys were conducted at 0◦, 3◦, 6◦, 9◦, and 12◦ on two swept wings, one with a smooth leading edge and one with a tubercled leading edge. Sweeping a tubercled wing resulted in an asymmetry in the strengths of the vortices produced by a single tubercle. Additionally, the strengths of the tubercle vortices increased with angle of attack. Below 3◦ there was little difference between the strength of the wingtip vortices of either wing, while above 6◦ the smooth wing produced a stronger wingtip vortex. For angles of attack 6◦ and below the tubercled wing reduced the profile drag coefficient, but had little effect on the induced drag coefficient. From 9◦ onwards the tubercled wing increased the profile drag coefficient and reduced the induced drag coefficient, ostensibly because of flow separation near the wingtip region. Corrected drag coefficients of the tubercled wing when producing the same lift coefficient as the smooth wing were calculated at 0◦, 3◦, 6◦, and 9◦. The same trends were found as in the uncorrected case, except at 9◦ where tubercles did not significantly affect the induced drag coefficient. The smooth wing produced relatively uniform profile and induced drag coefficient distributions along its entire span with peaks at the wingtip. Conversely, tubercles modulated the pro- file and induced drag coefficients along the entire span, with local maxima and minima in the profile drag coefficients forming in the troughs and over the peaks, respectively. Typically, tubercles produced local maxima and minima in the induced drag coefficients over the peaks and in the troughs, respectively. The majority of change in either the profile or induced drag coefficients occurred over the wingspan, but small changes were also observed in the wingtip region.