Preliminary Research On Effects Of Variable-Span Winglet On Wing Flutter Characteristics

Winglets can be used to inhibit wingtip vortex and to reduce the induced drag effectively, which guarantees the reduction of flight cost and improvement of climbing/landing performance. According to recent researches, induced drag holds 40% and 50% to 70% of the overall drag in the crusing and climbing/landing stages respectively. Traditional winglets are designed mainly for the cruising stage, while the effects of winglets in the climbing/landing stage are not as significant. Hence, it will be rewarding to design a morphing winglet which can act effectively in the entire range of flight.In this paper, span was selected as design parameter upon a thorough analysis of the influence of winglets on wing aerodynamic performance. A telescopic structure was designed to activate the varying of winglet span during flight. The height of morphing winglet will be increased to shorten the climbing and landing period. When the aircraft is cruising, the height of morphing winglet will be reduced so that the increase of wing root bending moment can be alleviated.Seven-Hole Probe(SHP) testing technology was used to analyse the wingtip flow structure of wings with span-variable winglet. The influence of winglet span on the velocity and pressure distribution of wingtip wake vortex was analysed. Results shown that height increment of winglet would increase the static pressure of wingtip vortex core significantly. Winglets could break wingtip vortex into several weaker vortex. These weaker vortex would dissipate quickly under the impact of viscosity, so that the intensity of wingtip wake vortex would be significantly weakened. Parameterized finite element models of morphing winglets and wings were established by MSC.PATRAN. Solution sequence 103 of MSC.NASTRAN was used to execute modal analysis on morphing winglet. Besides, vibration experiments and parameter identification were performed to verify the validity of finite element models. Solution sequence 145 of MSC.NASTRAN was used to run flutter analysis on wings with morphing winglets. Results shown that the wing flutter characteristics was deteriorated as a result of the winglet, as well as the increment of winglet span.