3D CFD Simulation of a H-Darrieus Turbine with Variable Pitch: A Quantitative Vorticity Analysis

Abstract

Vortices and dynamic stall play a critical role in the performance of vertical-axis wind turbines, often leading to significant energy losses. Active and passive control strategies can be employed to delay the dynamic stall, particularly at low tip-speed ratios below 0.5. In this study, three-dimensional Computational Fluid Dynamics simulations of a Darrieus H turbine equipped with a NACA 0018 airfoil are performed using a sinusoidal pitch control method. A vorticity analysis framework is developed to evaluate vortex transport, growth, and detachment, enabling a rigorous assessment approach. The simulations, conducted at 8 m/s wind speed, are validated against experimental data, showing less than 4% deviation. The analysis examines the correlation between vorticity dynamics and turbine performance across both the span and chord of the airfoil. At a tip-speed ratio of 0.5, where dynamic stall is dominant, the pitch control delays flow separation and increases performance by 238%. At a tip-speed ratio of 1.4, performance improves by 57%, although the flow shifts toward a drag-dominated regime in which vortex detachment plays a reduced role. This demonstrates that quantitative vorticity analysis remains effective under variable pitch and can identify stages of the dynamic stall, including imminent vortex separation, offering a basis for optimizing vertical-axis wind turbines.