Date of Award

6-14-2025

Document Type

Thesis

Publisher

Santa Clara : Santa Clara University, 2025

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Godfrey Mungal

Abstract

Winglets have been used to improve the aerodynamic performance of wings. They do this by decreasing the lift induced drag that is experienced by the wing. The winglet modifies the wingtip vortex generated by adjusting both its size, location and strength. Motivated by previous research on the manipulation of wake vorticity through the use of a forward or backward sweep discovered originally when investigating crescent wings, the presented work investigates the role of sweep, cant and slots on winglets. Sweep was first applied to positive and negative canted wings with a symmetric airfoil, the ONERA M6. The wing flows were solved using the CFD solver ANSYS Fluent, at a Reynolds Number of 5.55 ⇤ 106, and some surface visualizations were compared to wind tunnel experiments. Forward swept winglets with positive or negative cant experienced a decrease in lift at most angles of attack, AOA. Backward swept winglets increased lift at low AOA but only increased lift at high AOA for positively canted wings. Drag was more dependent on the cant angle, with positive canted winglets decreasing drag, while negative canted winglets increased drag at low AOA but decreased it at high AOA. Additionally, sweep alters the behavior of wing shear stress and change the shed vorticity. Specifically, forward swept winglets produce more negative curl than positive swept cases. To enhance the differences observed in flow behavior and wing performance a cambered wing was then investigated, using the NACA 4412 airfoil. This showed positive cant decreasing the lift induced drag factor, k, by 4.4% when compared to a wing with no winglet. Several fence type winglets were investigated using forward and backward slots to manipulate the shed vorticity. While the best performing winglet was an un-slotted full airfoil profile fence, decreasing the lift induced drag factor by 12.2%, slots were seen to help manipulate the shed vorticity. Specifically, backward slots shift the vortex core but increased its strength, while the forward slots decreased its strength but did not shift its position as much. The backward slot designs outperformed the forward slots, when measured by the change in the lift induced drag factor. The best performing slotted designs were the semi slotted winglets with slots only located on the upper half of the winglet and a flat plate on the bottom, while fully slotted winglets showed the best wake vortex manipulation.

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