Influence of leading edge tubercles on aerodynamic characteristics of a high aspect-ratio UAV

An experimental investigation was carried out to study the aerodynamic performance of a typical UAV whose wings were modified to incorporate tubercles on the leading edge. The aerodynamic characteristics of three configurations: a baseline (without leading edge tubercles), one with tubercles of constant wavelength and amplitude along the span (Case I) and the third with tubercles of varying amplitude and wavelength along the span (Case II) were evaluated using force measurements and surface flow visualization at Reynolds numbers (Rec¯) of 0.18 million and 0.27 million. At Rec¯=0.18 million, the wings with tubercles exhibited increased lift, stall angle and reduced drag as compared to the baseline over the range of incidences studied. Further, wing with tubercles significantly improved the aerodynamic efficiency (CL/CD) (up to 25%). At Rec¯=0.27 million, both the baseline and the modified wings exhibited identical lift characteristics, but the former had a higher drag. At both Reynolds numbers, the modified wings did not exhibit the hysteresis present in the baseline case. Additionally, the modified wings exhibited stable pitching moment characteristics even in the post stall regime. The Case II wing outperformed both the baseline and Case I wings. The results show that tubercles on the leading edge have beneficial effects especially when UAVs encounter sudden vertical gusts during operation.