Abstract
In this work, the aerodynamic performance and optimization of a vertical-axis wind turbine with a high tip-speed ratio are theoretically studied on the basis of the two-dimensional airfoil theory. By dividing the rotating plane of the airfoil into the upwind and downwind areas, the relationship among the angle of attack, azimuth, pitch angle, and tip-speed ratio is derived using the quasi-steady aerodynamic model, and aerodynamic loads on the airfoil are then obtained. By applying the polynomial approximation to functions of lift and drag coefficients with the angle of attack for symmetric and asymmetric airfoils, respectively, explicit expressions of aerodynamic loads as functions of the angle of attack are obtained. The performance of a fixed-pitch blade is studied by employing a NACA0012 model, and influences of the tip speed ratio, pitch angle, chord length, rotor radius, incoming wind speed and rotational speed on the performance of the blade are discussed. Furthermore, the optimization problem based on the dynamic-pitch method is investigated by considering the maximum value problem of the instantaneous torque as a function of the pitch angle. Dynamic-pitch laws for symmetric and asymmetric airfoils are derived.
Highlights
Benedict et al [31] designed a small-scale vertical-axis wind turbine (VAWT) with periodically varying blade pitch, and they studied the influence of the dynamic pitch on the performance of the turbine by using computational fluid dynamics (CFD) and experimental methods
The performance of a VAWT can be further improved by adopting a dynamic-pitch method
In order to validate the efficiency of the current dynamic-pitch optimization method, a three-bladed VAWT with the NACA0018 profile in [37] is taken as a computational ordertotovalidate validatethe theefficiency efficiencyofofthe thecurrent currentdynamic-pitch dynamic-pitchoptimization optimizationmethod, method, InInorder model
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Li et al [24] introduced an innovative truncated-cone-shaped wind gathering device that could improve the starting efficiency of a straight-bladed VAWT, and they discussed the influence of the device on the performance of the turbine by using both numerical and experimental methods. Benedict et al [31] designed a small-scale VAWT with periodically varying blade pitch, and they studied the influence of the dynamic pitch on the performance of the turbine by using CFD and experimental methods. Coefficients of lift and drag forces are fitted as polynomial functions of the angle of attack; the performance of the wind turbine is discussed theoretically, and expressions of the dynamic-pitch rule are presented This method can be extended to solve the aeroelastic stability problem of VAWTs
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