Computational aerodynamic analysis of annular wing unmanned aerial vehicles

Annular or Ring wing concept is a form of closed non-planar wing. The benefits of non-planar wing aerodynamics are well known and have been elucidated theoretically and experimentally. The widespread use of non-planar wings during the early years of human-powered flight had more to do with structural expediency than augmented aerodynamic efficiency. Non-planarity for a confined wing span may improve wing efficiency by capturing larger volume of air to generate lift impulse. In this study, the aerodynamic characteristics of an annular wing composed of symmetric airfoil section NACA 0012 is investigated for various aspect ratios ranging from 0.5 to 2. The computational modeling showed higher lift coefficient for aspect ratio of 2 and the resulting L/D ratio is observed to be best for this aspect ratio. To study effect of asymmetry, a cambered Clark-Y airfoil is considered as a wing section for the annular wing. The Clark-Y annular wing showed better aerodynamic characteristics with a stall angle higher than that of the NACA 0012 annular wing and attaining better L/D ratio at lower angle of attack. Further, a brief comparison between annular wing and conventional wing shows that a higher lift coefficient is observed for planar wing but annular wing admitted a higher stall angle. Computational results are compared with available theoretical results and experimental data. Owing to the benefits offered by cambered airfoil, an annular wing with Clark-Y airfoil is considered for an annular wing UAV design configuration with a V-tail empennage adopted for the UAV configuration.