Abstract
Vertical-axis wind turbines (VAWTs) have their rotor blades oriented vertically around a central axis of rotation. Unlike horizontal axis wind turbines (HAWTs), they do not require a mechanism to orient their blades into the wind, enabling them to capture wind from any direction. The absence of this directional adjustments makes VAWTs easier to install and to maintain. Furthermore, VAWTs can operate at a lower rotational speed, resulting in reduced noise emissions. This is one advantage making them more suitable for urban environments. The present paper discusses the procedure for calculating the aerodynamic loads on VAWTs using a three-dimensional panel method. Panel methods are based on potential theory and consider incompressible, non-viscous, irrotational flows. However, they do not account for flow separation effects but due to their fast computation time, they are primarily used for the initial aerodynamic design, such as the design of wind turbines. The paper first introduces the theoretical foundations of the numerical panel method, followed by an explanation of its application to vertical-axis wind turbines. By incorporating a rigid body motion, the rotation of the blades can be considered. Furthermore, to accurately reproduce the aerodynamics on the blades, a wake roll-up algorithm for the wingtips is utilized. The study focuses on a three-bladed vertical-axis wind turbine with NACA 0021 airfoils. For comparative purposes, transient numerical 2D simulations based on Computational Fluid Dynamics (CFD) were performed, using the OpenFOAM software. For the CFD simulations, the two-equation k-ϵ turbulence model was used. In order to minimize the effects of the VAWTs start-up process, multiple revolutions were examined in the simulations. The results obtained from the panel method and the CFD are compared, considering variations in forces and the rotor torque over the last revolution. The paper concludes by assessing the agreement between the results obtained from both methods and suggests how the panel method can be further developed with regard to accuracy and efficiency.
