Experimental Study Of Wingtip Vortex Control Via Multi-winglets And Tip Blowing

In this paper, the evolution of wingtip vortex of a wing with and withoutmulti-winglets and wingtip blowing were measured in the first place. A controllingstrategy combination of multi-winglets and tip blowing was proposed and has beenexperimental studied. The experiments were conducted in a low speed wind tunnel,the basic wing model was a rectangular NACA0015airfoil. Reynolds number (Re)defined by the chord length of wing and the flow speed was about5.3×104. Theblowing coefficient (Cμ) which defined as the momentum ratio of blowing and freeflow was0.017. The structures and evolution of the wingtip vortex were measuredusing PIV system (particle image velocimetry system). The angle of attack was fixedat10degree. The lift character of the wing with and without multi-winglets weremeasured by a force balance. The results shows that:1) Multi-winglets can divide thetip vortex into a series of co-rotating vortices. The merging of the vortices canaccelerate the dissipation of energy and reduce the intensity of tip vortex. The “+0-”configuration of multi-winglets improves the quality of local flow and decreases theeffect of the downwash flow generated by wingtip vortex. The lift coefficientincreases for α＞4°. The maximum lift coefficient increases by12.3%, and themean of instantaneous peak vorticity decreases by67%compared with that ofthe basic wing.2) Blowing can strengthen the “wandering” of vortex core, andchange the position of the tip vortex. Blowing depress the formation of thewingtip vortex to some extent but a negligible effect on tip vortex in the farfield. The blowing can not generate the structure of co-rotating vortices in thefar field, and lack of the capacity to dissipate the tip vortex. The “downwardblowing” configuration is of a superiority manner than that of blowingconfiguration else. It causes a smaller normal displacement of vortex core.This feature is quite suitable for the combination control strategy.3) Thecombination of the “+0-” multi-winglets and the “downward blowing” hasachieved a well control effect, the blowing enhances the interaction of theco-rotating vortices. The mean of instantaneous peak vorticity decrease by 37%compared with the “+0-” multi-winglets configuration, and by79%withthe basic wing. The control effect of the combinational strategy is subjected towhether the blowing could enhance the interaction of the co-rotating vorticesor not. The moving direction of wingtip vortex is a key. This work make useof the advantage of mature techniques, provide a novel and effective strategyfor engineering design to the low-speed aircraft wing tip vortex control. It isproven that the method is feasible to wingtip vortex control.