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 non-linear 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.

This paper proposes a correction method to improve the accuracy of traditional blade element momentum theory (BEMT) in predicting the mechanical power and power coefficient of horizontal-axis wind turbine (HAWT) blade. In this paper, the traditional BEMT incorporated with the Viterna-Corrigan (VC) stall/stall-delay model is proposed to improve the accuracy of power-curve prediction, by which its applicability is thus enhanced. For verification of the proposed method, three distinct types of geometries of HAWT blades subjected to different operations are studied with outcomes compared with experimental data. Two different wind turbines developed by National Renewable Energy Laboratory (NREL) were tested at constant rotational speeds in a full-scale wind tunnel to acquire performance data. As a comparative platform, another wind turbine designed by BEMT for this study was also experimented in identical environment but at variable rotational speeds. As expected, the results clearly indicate that the power-curve prediction is effectively improved by the proposed method especially in the stall region when compared with experimental data. Indeed, this study shows that the improved BEMT is an ideal means to accurately predict the power-curve used for designing an optimal HAWT rotor.