Modular structural design and performance analysis of multi-blade Darrieus wind turbines

Vertical-axis wind turbines (VAWTs) are promising for large-scale offshore floating wind power but face challenges in scalability and aerodynamic efficiency. This study proposes a modular multi-blade design for Darrieus turbines, dividing the outer blade into two parts to form a basic aerodynamic module for flexible optimization. Under the conditions of a tip speed ratio (TSR) of 4.0 and an inlet velocity of 12 m/s, orthogonal testing (OT) combined with computational fluid dynamics (CFD) reveals that the Δc chord length ratio has the greatest impact on the power coefficient, followed by Δr radius difference, while Δθ offset angle shows almost no influence. Further torque and flow field analyses identify the Δr=10 m, Δc=2 configuration with balanced performance and easier modular manufacturing. To utilize inner blade aerodynamics and support modular design, the radius difference of double-layer modular turbines is controlled at 5 m, 8 m, and 10 m, and redefine the offset angle as the installation angle. Based on this setup, performance comparisons are conducted between single-layer and double-layer modular turbines. The results indicate that the optimal power coefficient is achieved by a single-layer modular turbine with six blades of 4 m at a 150° installation angle, about 4.7% higher than a conventional design. However, considering that the double-layer configuration forms a stable triangular framework that facilitates manufacturability, assembly and transport, the double-layer modular turbine with Δr=8 m, Δc=2, and 150° installation angle is selected. Overall, this modular design significantly simplifies turbine fabrication, making it more practical for kilowatt-level wind power applications.