A general numerical unsteady nonlinear lifting line model for engineering aerodynamics studies

The lifting line theory is widely used for obtaining aerodynamic performance results in various engineering fields, from aircraft conceptual design to wind power generation. Many different models were proposed, each tailored for a specific purpose, thus having a rather narrow applicability range. This paper presents a general lifting line model capable of accurately analysing a wide range of engineering problems involving lifting surfaces, both steady-state and unsteady cases. It can be used for lifting surface with sweep, dihedral, twisting and winglets and includes features such as nonlinear viscous corrections, unsteady and quasi-steady force calculation, stable wake relaxation through fictitious time marching and wake stretching and dissipation. Possible applications include wing design for low speed aircraft and unmanned aerial vehicles, the study of high-frequency avian flapping flight or wind turbine blade design and analysis. Several validation studies are performed, both steady-state and unsteady, the method showing good agreement with experimental data or numerical results obtained with more computationally-expensive methods. Keywords: lifting line model, unsteady lifting line, 2D-3D coupling, lifting surface aerodynamics, flapping wing, horizontal-axis wind turbin