Multiobjective Airfoil Design for Airborne Wind Energy

Pumping-mode airborne wind energy systems (PM-AWE) consist of an airborne drone (UAV) that flies tethered to a ground station. The tethered UAV is expected to generate high lifts when reeling the tether out, descend with low force and damp gusts during take-off or landing events. These missions take place in unpredictable environmental conditions. Winds can be more or less turbulent, ground proximity prompts leading edge soiling and aerostructural effects induce shape deformations. Conventional aviation airfoils were not designed for these conditions but wing designers miss specialized alternatives. The need for specialized airborne wind energy airfoils was first identified by Venturato [1]. He redesigned the Clark Y airfoil with a genetic optimization approach based on a simple performance goal and a RANS CFD solver. This type of CFD model cannot capture important physical phenomena like laminar bubbles or turbulent transition but Venturato’s work had the groundbreaking merrit of raising awareness about specialized airfoils. Here we present a collection of airfoils designed for the needs of the airborne wind energy industry. The design exercise builds upon an established airfoil optimization framework with a proven track record in the conventional wind turbine industry [2,3,4,5]. The method is known to provide a broad coverage of the design space thanks to the use of a CST parametrization, a tuned version of the RFOIL viscous-inviscid solver and multi-objective genetic optimization algorithms. Candidate airfoils are assessed in terms of conflicting structural and aerodynamic goals. Pareto fronts quantify compromises between glide ratio, maximum lift, building height, stall harshness and resilience to leading edge soiling. Finally, desirable pitching moment characteristics are framed within the broader question of planform design, a question on which we hope to engage the audience in a lively discussion.