Aerodynamic analysis of variable cant angle winglets for improved aircraft performance

Aircraft performance is highly affected by induced drag caused by wingtip vortices. Winglets, referred to as vertical or angled extensions at aircraft wingtips, are used to minimise vortices formation to improve fuel efficiency. This paper describes a wind tunnel experiment and a Computational Fluid Dynamics (CFD) analysis, performed on a rectangular wing prototype (with and without winglet) of NACA 65₃218 aerofoil section. The objectives of the analysis were to compare the aerodynamic characteristics and to investigate the performance of winglet at cant angles 0°, 30°, 45° and 60° at various angles of attack (AOA). The experimental analysis was performed in a closed-loop wind tunnel at sea-level conditions and free-stream velocity of 35 m/s. The CFD simulations were performed at low subsonic flow speed in ANSYS CFX solver using Finite Volume Method. Spalart-Allmaras turbulence model and 3-dimensional unstructured tetrahedral mesh were used to compute the flow around the model. The aerodynamic characteristics of lift coefficient (C_L), drag coefficient (C_D) and lift-to-drag ratio (L/D) were compared and it was found that each winglet configuration at a particular AOA had different C_L, C_D and L/D values, indicating that fixed winglets do not provide optimum aircraft performance at different phases of flight.