Wake Alleviation Properties of Triangular-Flapped Wings

Abstract

Thewakealleviationproperties of wingswith outboard, triangulareapextensionsareestimated usingdatafrom particle image velocimetry. The experiments are conducted in a towing tank at chord-based Reynolds numbers of O O(10 5). The triangular-eapped wings generate two unequal strength, counter-rotating vortex pairs that have circulation strength ratios ranging from i 0.4 to i 0.7. Introducing the oppositely signed eap vortices near the tip vortices causes arapidly growing instability to occur between the vortices on either side of the wake. The resulting nonlinear interactionsbetween thevorticesresult inawake that ishighly three-dimensional and incoherent. These effectsarereeected inamarked decreaseinboth therollingmoment and downwash on asimulated followingwing. To determine the wake alleviation properties of the triangular-eapped wings, their wakes are compared to that of a conventional, rectangular wing. For all of the experimental runs, the wakes of the triangular-eapped wings have maximum rolling moments and downwashes that are substantially less than those of the rectangular wing. The results indicate that the instability in the wake of the triangular-e apped wings offers a possible mechanism to reduce signie cantly the wake hazard problem.