Wind turbine unsteady aerodynamics and performance by a free-wake panel method

Abstract

Abstract The performance of a horizontal axis wind turbine in axial and yawed flow are investigated by a free-wake, unsteady, three-dimensional aerodynamic formulation. Under the assumption of attached-flow conditions, predictions in terms of blade(s)/rotor aeroloads and velocity field downstream the rotor disk are compared with experimental data concerning the Mexico rotor, namely a three-bladed model tested in the large open jet facility of the German Dutch Windtunnels DNW. The numerical/experimental comparison herein addressed is aimed at highlighting drawbacks and potentialities of aerodynamic formulations based on the Boundary Element Method for incompressible subsonic flows around wind turbines that, surprisingly, are barely used respect to marine current turbine applications. The accuracy of numerical outcomes respect to experiments and other widely used approaches (like lifting-line, vortex-lattice and blade element theories) proves that panel method rotor aerodynamics is accurate enough as long as severe flow separations do not occur on turbine blades, thus avoiding time-consuming CFD analyses, often not compatible with a preliminary design of the device. In addition, performance of the Mexico model-scale rotor in two operating conditions are discussed. They concern the presence of an extreme vertical shear and the installation of the rotor on a floating platform undergoing a pitching planar motion.