Boosting H-Darrieus vertical axis wind turbine performance: A CFD investigation of J-Blade aerodynamics

Abstract

• J-blade design significantly improves VAWT self-starting torque by 142 %. • Grid refinement ensures solution independence and numerical reliability. • CFD framework ensures convergence with optimized azimuthal increments. • Gromeka acceleration vectors used to assess wake stability. • The J-blade offers a promising solution for efficient urban wind energy applications. This study investigates the aerodynamic performance of a J-shaped blade design for H-Darrieus Vertical Axis Wind Turbines (VAWTs) to improve self-starting capability and overall efficiency. A two-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) computational fluid dynamics (CFD) model was developed using ANSYS Fluent 19.2, validated against experimental data, and employed to analyze airflow around the J-blade geometry. The numerical results indicate that the J-blade achieves a 142 % increase in starting torque at a low tip speed ratio (λ = 0.2), addressing a key limitation of conventional VAWT designs in low-wind environments. Additionally, at an optimal λ of 1.6, the J-blade maintains comparable torque to the conventional NACA0015 airfoil, while reducing vortex shedding and wake turbulence intensity by 12.3 %, leading to improved torque uniformity and lower mechanical stresses. Mesh independence studies confirmed that a grid size of approximately 1.2 million cells provides reliable results with <1.2 % deviation from benchmarked studies. The J-blade design demonstrated higher lift contribution due to its modified trailing edge, enhancing aerodynamic performance without significantly increasing drag. At λ = 2.5, minor performance trade-offs were observed, with the J-blade experiencing a 3.6 % reduction in torque compared to NACA0015. However, the overall findings suggest that J-blades can significantly enhance VAWT efficiency, making them well-suited for urban wind energy applications.

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