Effect of winglets induced tip vortex structure on the performance of subsonic wings

This paper presents the comparative study of the effectiveness of three different winglet designs in reducing lift induced drag by changing the number of vortices and vortex distribution at the wingtip and correlating it to the aerodynamic characteristics of the baseline wing. The best three winglet geometries are appended to wings of different aspect ratio to further study their effectiveness in reducing drag and augmenting the lift coefficient. Computational simulations were performed on Ansys Fluent V15 using the Reynolds Averaged Navier-Stokes equations coupled with the k-ω SST turbulence model to study the three dimensional flow and vortex structure about the half wing. The simulation shows that there is a strong relationship between the size of the tip vortex and the aerodynamic parameters such as lift, drag and pitching moment of the wing. The multi-tipped wing is the most effective at dispersing the vortice energy and reducing the induced drag. Optimization of the number of tips was found to be crucial to increase the lift coefficient while reducing the contributions of frictional and vortex drag. Although the lift was found to be increasing with the number of tips, the rise in frictional drag due to wetted surface area is a limiting factor towards aerodynamic efficiency. The results show that the multi-tip-4 is most capable at increasing the lift coefficient, but is surpassed by multi-tip-3 in lift to drag ratio. As aerodynamic efficiency is key for improving flight range and duration, it is concluded that multi-tip-3 is the optimum winglet for the given design conditions. The baseline wings show maximum performance at higher aspect ratios. Overall, winglets are found to be more effective at lower aspect ratio and provide highest improvement in aerodynamic efficiency at a moderate aspect ratio of 10.